I don't know any obvious reason not to
A fairly obvious reason is that to generate a tulpa you need to screw up you mind in a sufficiently radical fashion. And once you do that, you may not be able to unfuck it back to normal.
I vaguely recall (sorry, no link) reading a post by a psychiatrist who said that creating tulpas is basically self-induced schizophrenia. I don't think schizophrenia is fun.
A fairly obvious reason is that to generate a tulpa you need to screw up you mind in a sufficiently radical fashion. And once you do that, you may not be able to unfuck it back to normal.
This is a concern I share. However...
I vaguely recall (sorry, no link) reading a post by a psychiatrist who said that creating tulpas is basically self-induced schizophrenia. I don't think schizophrenia is fun.
This is the worst argument in the world.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.