Obamacare requires employers to pay for healthcare if you work more than 25 hours (of course, some businesses like McDonald’s have an exemption, anyway). Anon is claiming his employer is intentionally cutting hours to avoid healthcare costs. I have no idea whether it’s actually very common or not.
Who decided that’s how downvoting should be used? There is no official rulebook (especially on the fediverse), and etiquette is decided as a group, but there isn’t clear consensus on this.
The technical function of the downvote is to push the comment down far enough that people won’t see it. And so people will continue to use it as a way to communicate that they do not approve of the comment. And telling people to stop downvoting comments they don’t like is trying to enforce a rule they never agreed to.