What if doing housework is actually bad for people?

I'm not sure what you mean by it being 'bad'. Leading to unhappiness? As opposed to even more unhappiness due to a messy house?

It's certainly something that people have to be trained into

I disagree with this in it's generality. The ability to to household tasks needs to be trained. Establishment of the habit is another thing. An approach that leads to a relaxed approach to 'chores' depends on the motivational structure of the child (if you imply parenting).

An intrinsically motivated (on this kind of tasks) child will likely want to do the tasks if it clear that this is necessary to achieve it's own goals. So if household tasks are routinely coupled to some things the child want/needs for itself like clothing of its choice, access to materials, support in its projects..., then it will do these tasks (as long as it doesn't perceive the dependency as arbitrary, constructed, forced or unfair. Prototype example is my oldest son who has lots of projects for which he needs space and materials.

An extrinsically motivated child (more like my second oldest) can be influenced via frequent positive feedback for performing these tasks.

a lot of people resist doing [it]

Sure. I can confirm that my sons resist doing it in many circumstances. But the details differ widely.

No one does it for the fun of it.

Gamification is possible. Though not always. And it has a cost in terms of efficiency. But you don't need fun to want to do it and feel satisfaction from completing it.