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Not the person you're asking, but I thought the [-] acted as a downvote button and hid the offending content at the same time.

If it isn't, why do some controversial comments get into a lighter font?

Once you get a certain level of karma you get the ability to downvote comments - lighter font means people downvoted it

You unlock the ability to downvote posts and comments at 500 karma points I believe

Comments yes, posts no. Post downvoting either does not exist or has much higher karma threshold.

You can flag posts, though.