The question has nothing to do with an entirely optional vacation. You've bought a ticket for a funeral, a job interview, etc. Why should it be ok for the airlines to bump you off your flight when you have bought a ticket? Just so they can make a little bit more money when people occasionally don't show up?

To be fair. Involuntary bumping is happening very rarely.

Airlines don't have an interest to bump passengers. At least in Europe this can be relatively costly as in up to 600EUR compensation per passenger. Add hotel rooms, multiple restaurant visits, taxis and communication costs to that. Add the image loss if this happens too frequently.

Airlines employ extremely complex math and statistical models to avoid bumping passengers, while filling the plane to capacity and mostly it works out. If it doesn't they usually find volounteers, who are willing to be bumped, provided that they are fairly compensated and provided with a reasonable alternative.

What if you can't afford a plane ticket to attend a funeral? Should airlines give you one? Without overselling flights travel would cost more for everybody (at least in theory).

Job interviews are readily rescheduled if you're bumped against your will.

Airlines already have bereavement flights that give the bereaved priority and extra flexibility.

We already have regulations that compensate people who are bumped against their will so it's not in the airlines best interest to do so, it's expensive.

BTW, my mom missed her dad's funeral due to the 1981 air traffic controller strike.