Why do we have to vote?

Why are people quick to judge when you choose not to vote? If people don't feel strongly between either candidate, why should he/she feel pressured to have to choose? I've done my homework, & I still don't feel strongly either way. It's fine & dandy if you feel strongly towards 1 party or another, but I just find it unnecessary to make others that are indecisive, or rather, decisive about not liking either candidate, feel like they HAVE to make a decision. I'm not voting this election, & I shouldn't be criticized for it.