A vote to treat people badly is _absolutely_ a good reason to be angry at someone.
If you're voting to take away people's healthcare, or to discriminate against them based on who they love, or their gender, then of course they are angry!
Still no excuse for physical violence. Votes are how we make decisions in our society. You don't always win. You can argue your position all you want, but you don't get to intimidate others with violence.
OP said the fight was about a different viewpoint, not voting for a different party. There's a whole world of viewpoints outside the two dominant political parties in the US.
"I think your kind is an abomination that should be hearded into camps and slaughtered", is a political opinion that might well lead to a fight or 'anything in between'. It has little to do with a vote. Some 'conservative' people now believe it's ok to voice those opponions at work. We don't know what was said based on the parent, and we don't know how it escalated... so maybe that's it?
Some people won't be cowed by a publicly aggressive racist... I'd tell my boss that I'm uncomfortable working with them. I'm not a snowflake, if someone else can't handle my speach and the resulting consequences of their own.
If you're voting to take away people's healthcare, or to discriminate against them based on who they love, or their gender, then of course they are angry!