This isn't exactly addressing a bad argument per se, but I reserve the right to depart from this blog's theme whenever I damn well please. Also it follows along the general theme of elevating the level of discourse.
I'd just like to speak a bit on a piece of my personal philosophy. It's very simple, and I'm sure you've heard it before, but its implications are wide and honestly it can be more difficult to follow than you'd first imagine.
Err on the side of caution.
This is a very useful thing to keep in mind whenever making risky decisions, but I think that it's something that can be viewed as an approach to dealing with the world. Granted, there are going to be situations where haste and risk are necessary, but any good rule has its exceptions, and everything should be met with discretion.
Another more specific way to say this that relates better to our politics:
Only makes assumptions to your detriment.
This is about staying intellectually honest as you disagree with a person, as well as resulting in a much more sound and thoughtful argument. If you can still thoughtfully debate for a point while giving favour to your opponent's viewpoint whenever as assumption is required, then not only can you be sure that you were intellectually honest in presenting your opinion, but also that your point will stand up to far more scrutiny than it would otherwise.
If you are unable to make an assumption in a way that favours the other viewpoint (it doesn't have to be by much), then you must either find a way to reach your conclusion without the assumption or at the very least be honest about how big the assumption is.
I got a bit distracted while writing this, so I can't remember if I said everything I wanted to. So as always, if any elaboration is required, please say so.