Well, yeah. The primary worry among tulpa creators is that it might get pissed at you and follow you around the house making faces.

They ought to be at least somewhat concerned that they have less brain for their own walking around the house.

And what, pray tell, is the salient feature of mental illness that causes us to avoid it? Because I don't think it's the fact that we refer to them with the collection of syllables "men-tal-il-nes".

You don't know? It's loss in "utility". When you have an unknown item which, out of the items that you know of, most closely resembles a mushroom consumption of which had very huge negative utility, the expected utility of consuming the unknown toxic mushroom like item is also negative (unless totally starving and there's literally nothing else one could seek for nourishment). Of course, in today's environment, people rarely face the need to make such inferences themselves - society warns you of all the common dangers, uncommon dangers are by definition uncommon, and language hides the inferential nature of categorization from the view.

If you had looked into the topic, you would know the process is reversible.

The cases I've heard which do not look like people attention seeking online, are associated with severe mental illness. Of course the direction of the causation is somewhat murky in any such issue, but necessity to see a doctor doesn't depend on direction of the causation here.