Smart people, or at least those whose brains have good first gears, use their speed in thought to overpower others. They’ll jump between assumptions quickly, throwing out jargon, bits of logic, or rules of thumb at a rate of fire fast enough to cause most people to become rattled, and give in. When that doesn’t work, the arrogant or the pompous will throw in some belittlement and use whatever snide or manipulative tactics they have at their disposal to further discourage you from dissecting their ideas. Scott Berkun
I believe this applies to many blog commentators, and not just the smart ones. They hop, skip, and jump from argument to argument and topic to topic, never letting you pin down the flaws because by the time you get there, they're already somewhere else.
Scott Berkun has some ideas about how to prevent people from doing this. Although he's talking mostly about working on a software development team, I think his advice is relevant to all of us.
So your best defense starts by breaking an argument down into pieces. When they say “it’s obvious we need to execute plan A now.” You say, “hold on. You’re way ahead of me. For me to follow I need to break this down into pieces.” And without waiting for permission, you should go ahead and do so.
First, nothing is obvious. If it were obvious there would be no need to say so. So your first piece is to establish what isn’t so obvious. What are the assumptions the other guy is glossing over that are worth spending time on? There may be 3 or 4 different valid assumptions that need to be discussed one at a time before any kind of decision can be considered. Take each one in turn, and lay out the basic questions: what problem are we trying to solve? What alternatives to solving it are there? What are the tradeoffs in each alternative? By breaking it down and asking questions you expose more thinking to light, make it possible for others to ask questions, and make it more difficult for anyone to defend a bad idea.
No one can ever take away your right to think things over, especially if the decision at hand is important. If your mind works best in 3rd or 4th gear, find ways to give yourself the time needed to get there. If when you say “I need the afternoon to think this over”, they say “tough. We’re deciding now”. Ask them if the decision is an important one. If they say yes, then you should be completely justified in asking for more time to think it over and ask questions.
I realize now that this technique is what I always try to do, but I've never spelled it out before. I try to keep the focus on a single aspect of an argument until it's settled. I don't let my opponent shift the goalposts, gloss over an assumption, or use fallacious logic in order to befuddle me.
The best part is that you can often (well, "rarely" is probably more accurate) convince your opponent that they need to rethink their position, since it's basically a house made with shoddy materials on a shaky foundation.
In his essay, he also includes the reasons he believes smart people defend stupid ideas: they inherited them from parents, they've gotten away with defending them before, groupthink, short-term thinking, desire for an idea to be true, following stupid leaders, etc.
I think religious people are particularly likely to hold bad ideas due to tradition, following stupid leaders, and the desire for an idea to be true.