I suppose downvotes may serve a purpose, but I have seen more abuse of the downvote than it being used productively. As for me, I do not downvote. I have received a few downvotes in my five years, but try to defuse or ignore them. It seems negative votes only encourage negativity.
It always depends where you look. There have been some very abusive people on this platform over the years and without downvotes, they would still be here doing it. That kind of behavior sets examples and poisons the platform too.