Is this forum for certain denomination of Christians only or are all welcome?
I want to spell out clearly the answer to this part of your question.
- All Christians are welcome, regardless of their faith community.
- Non Christians are also welcome.
The only requirement is to participate within the boundaries already established for the SE model, and the community's agreed ways to avoid the kind of noise and bickering that is all-too-common on the rest of the internet. Since the original beta version of this SE, which was back in 2010 or so, it has taken a while to figure out, collectively, how to achieve those objectives while addressing this potentially explosive topic: Christianity.
Lastly, it is SE-wide policy that a comment is not required when casting a down vote, and I often find that as frustrating as you do. I usually provide a comment if my down vote is linked to how the question is unclear, or I have a particular suggestion on how to improve the question. (Likewise with answers). But there is no requirement to do so.
I am now going to something a little silly, and quote myself:
Because this community is not interested (collectively) in the great, 1900-year-long shouting match of "I'm right, you splitter!" -- "No, I'm right, you heretic!" this is a unique internet space where I can engage warmly with my fellow believers from across the denominational spectrum.
And I'd hope it stays that way.