"Republicunt": why use terms like this?

[CapnAwesome]

People against same sex marriage, for example, tend to be homophobic 

You can't be against same sex marriage, and not be a homophobe.  I mean wanting to deny people their rights for your own religious purposes?  That's homophobic in and of itself.  Social Conservatives are just shitbags, and there's no reason to dance around that fact.

Even if all that is true, do you think about your end goal? What are you trying to accomplish? If it's changing someone's mind, calling them a shitbag is just going garden them in their position. If it's changing the mind of a third party observer, it's not doing much for your case either.

Ultimately what you are left with is that it makes you feel good to do it. Which is the oldest reason anybody insults anybody.