You'd want to flag an answer that is actively harmful to the site.
There are obvious cases for this designation:
- Spam answers: people posting self-promotional links without disclosure
- Answers that aren't: some people don't understand how editing, voting, or commenting works and will leave anything but an answer in the answer section ("Thanks for the answer!", "I have this question too!", "I have a different question, it's this")
- Answers that clearly fail the Miller test: this is a bit of a tough one, but I think there's stuff any reasonable person, religious topics or not, would find offensive and would drive away people from the site if they're left to stand.
Then it starts getting into judgement calls: down-voting is the default action on answers that aren't useful, but one should also look at whether an answer is just so bad that it being there is driving people away from the question or the site.
In this case, and given how early we are in beta, I'd say a person copying-and-pasting Wikipedia to answer questions drives away potential experts, who might view this site as nothing more than Yahoo! Answers. If commenting and down-voting doesn't prompt a user to revise their answer, I would consider flagging the answer as not an answer so it could be deleted.