Well, John Hardly, you sure pointed out a major concern up there:
" portraying other's beliefs for them (in order to "shoot them down")."
Two problems are involved. 1) People who don't really understand their own beliefs and the basis on which they believe what they do, so they end up with awkward explanations of their own system...and 2) People who, as you say, try to portray other's beliefs FOR them....and may be no better at it than those they're criticising.

In my years at Mudcat sticking my nose into these types of discussions...on religion as well as other 'hot' topics, I have always tried to avoid telling someone "you are wrong...it can't be that way or can't exist". But I do know a little bit about how logic and arguments work, and I can often note when an attempted claim or explanation is not easily defendable, given the premises of the assertor. Not a wholesale "you are wrong", but "you have made errors in your defense" or similar problems.

    It is a sort of mantra in these matters that the burden of proof is on the assertor. If you just say "this is what I believe", all I can really do is shrug and say "I don't". But if you say "I KNOW this is how things work and/or why", you should be prepared to defend it.
   (I had two Jehovah's Witnesses come to my door and make assertions about how I should conduct my life, based on certain Bible verses. I said "I don't really accept the authority of the Bible for these reasons....A,B,C"...so they went away and came back with a more learned Elder who tried to reply to my objections by reading me different Bible verses! He just didn't get it....he could not comprehend why anyone would/could/dared look beyond the Bible for ultimate answers!) At this point, there is simply nothing to say...and if they had left me alone, I would NOT have said anything. I disagree with them, but I do not go over to their church a few blocks away, knock on the door, and try to sell them Atheism or Agnosticism. (lordy, what an image!)
   I cannot prove they are wrong in their beliefs....but I am not trying to. THEY are out making claims and assertions about eternity, souls...etc....yet they get a bit grumpy when I offer my picky analysis of their assertions.

ah, well....it is good mental exercise when I get a couple of new ones....