If someone's completely dissilusioned with all candidates and refuses to vote, they can then deny having any active responsibility if the next government is a disasater.
I voted in the last general election here; I knew that they weren't going to win, but I agreed with their policies. A wasted vote, perhaps, since it didn't change anything... but if everyone took that approach, then nobody would vote and nothing would get done.
Refusing to vote, I think, doesn't disbar someone from commenting on political matters; just like conscientious objection doesn't mean you can't have a valid opinion on war. We're all affected by the outcomes, whether we're a part of the process or not.