I can only echo the other answers that being a dick on Stack Exchange is never appropriate.
However, bear in mind that bad science and gross misrepresentation actually threatens lives. For this reason, you shouldn’t give quarter in public discussions.
To quote John Beddington, Chief Scientific Adviser to the UK Government:
We are grossly intolerant, and properly so, of racism. We are grossly intolerant, and properly so, of people who [are] anti-homosexuality … We are not […] grossly intolerant of pseudo-science.
I’d urge you [to] be much more intolerant.
(Emphasis mine)
Beddington contradicts Phil Plait in this point, and I think Beddington is right.
Once again, this does not apply to the q’n’a format of Stack Exchange. But in public discussions, if being grossly intolerant of bad science is seen as a dick move (and it often is), then so be it.