Are there any good reasons to start allowing personal opinion?
Is PO the alternative usually being advocated when users oppose a policy on "identifiable position"?
No, for the simple fact that we don't care what "you" think, we care what groups of people think. (See #6) Likewise, personal opinion falls short even of the amazingly low bar we have for notability criteria.
Good answers can definitely reflect your personal opinion, but it's the sourcing that matters. If you are drawing from standard sources of theology, the 'personal opinion' piece pretty soon either gets rooted in Scripture, Tradition, or Reason - and hence can and should be readily identifiable - or else relegated to personal experience - which will almost always be too localized to be of any help.
OK
Lets start with the most important thing.
Personal opinion is off topic here and any answers that contain personal opinion that cannot be identified as being held by an identifiable Christian group or established Christian doctrine should be downvoted outright, maybe even flagged, though that's a hairier situation
That's our ideal. However, reality introduces some problems:
Site policy is not an effective means to control how people vote. In other words, I can make a statement like the above, but if people don't vote that way it's kinda hard to enforce that kind of standard.
Flags are great if it's obvious something is wrong. However, there are only two options for flagging answers that aren't offensive or spam: Very Low quality and Not an Answer. Again, it's up to the community to police site policy not the moderators.
Community deletion is a high bar and very hard right now. We have like 3 people who aren't mods who can delete downvoted answers. That's it. Which means that flags are the only way we can delete things this leaves moderators making more judgements about content than they are really meant to.
So where does that leave us?
As a community we have decided that rather than trying to police answers (hard) we should police the questions that solicit the personal opinion answers. The reasons for this are obvious:
Community closure of questions is pretty easy, we have a good number of 3k users.
Closure by a moderator is a barrier that is far easier overcome than deletion by a moderator
Question closure is a lot friendlier to new users than answer downvotes or deletions.
Question deletion is largely automated if a user abandons a low vote question (0 or lower).
Now, unfortunately this kind of moderation effort still requires that the community be very involved. We have almost 40 users who can cast close votes, however many of our most active users are still well below the 3k rep threshold needed to cast those close votes.
In the meantime, if you'd like to help with enforcing this site policy please make sure you are flagging questions that do not meet this site's quality standards (no identifiable doctrinal/denominational view point, aren't quality, duplicates, are unclear x, solicit personal opinion, etc).
By flagging these questions you get them into the close queue which is typically well monitored. Remember that not everyone manages to read every question that comes across (not even the moderators).
Last thought. The other answer on this question addresses a perceived inconsistency in moderation styles on this site. I might mention that forming such an opinion in a short time period may not be accurate.
But more importantly, SE is not designed to be moderated by just a couple of users who've been given badges, guns and had diamonds stapled to the end of their user names. It's designed to be moderated by the community itself (did you know that he first iteration of stack overflow didn't even have any moderators at all? mods were a late edition to the concept). There are relatively few diamond moderators on this site compared to the number of users, if we don't have high rep users enforcing site policy this site will not be the best it can be.
Addendum:
We often use the "Christian group" language, and I think that might be the hangup that motivated this post. What we're trying to do with that verbiage is pin folks to an existing set of doctrines. Most groups have a common set of doctrines that they share. The problem is that trying to get someone to identify the doctrines they are discussing requires them to do even more research than simply identifying a group they identify with. What we're really after is trying to get folks to narrow down the pool of scholars to draw from for answers.
If you want to know about Calvinism, then there is an established pool of authors. If you want to know about Baptists theology than there is an established pool of authors. If you want to know about Christianity in general than the pool of authors is simply too broad to draw from with any kind of certainty. There are literally hundreds of books and thousands of articles on just about any topic you can think of. What criteria should we use to narrow down the authors? Shouldn't that be up to the question author?
Answers should only include what we know to be true.
The alternative is that our upvotes and downvotes mean nothing because it is impossible to judge opinions (except based on their poetic qualities) and feelings are neither right nor wrong.
No, personal opinions should not be allowed on the site.
No, suggestions that moderation is overly stringent in demanding "identifiable positions" in questions and answers does not mean that going easy on PO were ever being advocated, at least by myself. Best construction, please.
Here's an example of an abuse of "personal opinion." I know one Twitter personality who has written books explicitly rejecting inspiration of scripture, yet goes on Tweeting about what "God wants". This is nothing but personal conjecture. We wouldn't want any activity like that here.
But here are some reasons why "identifiable perspective" as a rule-- certainly as a rule only actively enforced by ONE of the current moderators-- does not make for a healthy Christian site, or a healthy "academic format" Q&A site.
1) Martin Luther's first day. There's a scene in the Luther movie where he is in a classroom and you can see that he spark of the Reformation is in his eyes. His instructor is giving the position of the Roman Catholic hierarchy. Luther starts interrupting the instructor to rebut him. But he neither says, "God wants" without citation, nor does he give any identifiable position. It's something he thinks of on the spot, but involves quotations from Scripture and the church fathers. He's the first and only (on that day) to have the opinion.
2) C.S. Lewis' Mere Christianity. Recently someone in meta expressed a desire that Jives could join us. He has great Answers as to what sin and grace are. The strength in his positions was that he was able to either go beyond denominational bickering, or summarizing the best truths from different views.
3) Don't dare ask Lutherans for the Lutheran position. Lutheranism, in practice, at least on the internet, is overrun with persons who posit one extreme political position or another as Lutheranism or the Gospel. So while a perspective of needing to know an Answerer's perspective may be useful to a devout Catholic or Southern Baptist, I believe it's just as likely to cause rancor as to be a balm against it.
4) Was Charles Finney crucified for you? Finally, we do get genuine seekers, and we do get ornery folks trying to score a point (future genuine seekers) here. Isn't it the worst possible evangelistic witness, to a question that could be answered with a great quote from C.S. Lewis or Bono, to say that "question is on hold because no identifiable perspective was requested."