If you start with upvoting and downvoting, FR risks becoming another Reddit.
I don't know anything about "Reddit". I presume from your comment, that this would be a bad thing?
What is the downside of upvotting and downvotting? I've seen it on other websites. I've got something like 43,000 "upvotes" on one of them.
I think they are kinda like monopoly money. They aren't really good for anything, but you can have fun getting them.
Downvotes? I've got plenty of those too, but they are way outnumbered by my upvotes.
I think "upvotes" are an acknowledgment of sorts that other people saw some bit of merit in something you have said.
I think that makes most people a tiny bit happier.