This is community-evaluated content, and downvotes are a tool used for evaluation. So I think they make sense.
That being said, I don’t believe they should be public by default. People are nuts these days, especially online, and I don’t want to catch an online stalker or some nazi sliding aggro into my DMs because I downvoted their post.
free as in beer yes, but not free as in the amount of time you will spend trying to install drivers for all your peripherals and then find yourself being castigated for asking for help in a GNU/Linux forum and being criticized by forum oldheads for not using the search even though you did use the search, but it only led you towards other threads which also all ended with terse messages to use the search, and then you’re directed to a 1200+ page megathread on driver issues and told to spend the next three months parsing through it repeatedly before daring to post again.