Vinegar is an effective fabric softener, it removes buildup from modern detergents. I don't use it because I don't use any softeners, but it's a great alternative to fabric softener because it's not highly flammable (fabric softener leaves a flammable waxy coating behind) and many people find it helpful for hyperreactivity disorders they may have.

I'm sensing your hostility towards the "crunchy" space here, and I'm with you. But vinegar as softener is not the hill to die on. Go after the people using it to "clean" their counters 🤮

Eh. Over a loooong period of time large amounts of vinegar can damage hoses, usually that's the amount of vinegar people put in to "sanitize" the machine though, not their clothes.

1/2 or 1 cup of vinegar per wash added as a softener isn't going to damage the machine fast enough to make a difference unless you have a machine that's actually made well enough to last 10 years; If you have one of those machines, you'll probably want to replace the hoses anyhow at some point.