What is the reasoning behind downvoting lowering the voters reputation? Isn't this supposed to be a helpful action?
Note that only downvoting answers lowers your reputation, you're free to downvote questions as much as you like.
In a nutshell - although downvoting is a useful and necessary part of the system, it tends to elicit hurt feelings and hostile reactions at a more individual level, as I'm sure most people have noticed. It's also prone to abuse. We want people to focus on downvoting the stuff that's truly low-quality or simply wrong, as opposed anything that happens to rub them the wrong way. Or worse, trying to game the system by downvoting everyone else's answers everywhere.
Think of it as keeping the honest people honest; the cost is so small, it really shouldn't hold you back from downvoting something that really deserves it.