The simple version is that everyone wants to raise the debt ceiling, because it would be beyond stupid not to raise it. The consequences of raising it are that the status quo continues. All parties involved like the status quo. The consequences of not raising it are unknown, but probably include a major freakout in all world markets, and possibly another freeze in credit and a new recession.
The slightly more complicated version is that the GOP thinks they can win concessions out of Obama by pretending that if he doesn't give them what they want, they'll let the US default and damn the consequences. There are good game theoretical reasons for them to do this if they think he'll blink first, and the precedent is that he will. So they're highly motivated to pretend that they're willing to default.
Moving a little further out, we have Crazytown, Population: Yes. One consequence of the Republicans pretending to be insane (and communicating their insanity to all and sundry) is that in some cases, it can infect people with actual insanity. Thus, stuff like that newspaper columnist talking about how we should actually lower the debt ceiling. Or Facebook posts about houses full of sewage. (And, quite probably, a portion of the GOP House) These people don't understand the actual consequences of defaulting, and so think that they can make some kind of principled stand here. The mainstream Republicans are basically ok with this as it lends some credibility to their insanity plea, but it could also bite them (all of us, really) in the ass if they can't whip people back into line.
