I've played volleyball for years. A footfalt during serving, even if it's just a toe on the line, meant you lost the point. No discussion. We accepted that. The rules are clear.
The difference between volleyball and tennis: there is always a referee in volleyball and almost never in tennis (unless you're a pro). At least that's how it is in my area. So most of us are not fully aware of making foot faults because they don't get called, so we keep making them, and it has become very hard to point it out to someone.
On top of that, it's just very hard to see them if you're the opponent. Self officiating is fine when it comes to line calling, but since a foot fault is on the other side of the net, where the other guy makes all the other calls, it feels very invasive to call a foot fault.
My personal opinion is that a foot fault SHOULD be called, but usually CANNOT be called, because you just can't see them. I happen to have a team mate who makes a LOT of foot faults, so during competition play I am not really in the position to say something if one of the players of the other team does it. Or rather, it wouldn't be smart.
The practical thing to do is to mention it in a friendly way if you can clearly see that someone does it repetitively. During singles, I just can't tell. During doubles, I just don't pay attention to this. Maybe I should.