The advice to not create lasting thought forms (also called TULPAS) comes from the experience of one person. I forget her name.

She said that a thought form being she created became evil and turned on her after a couple of months.

This advice applies to creating Tulpas, or servitors, and not objects.

Other magicians of note do not give the same warnings.

I have experimented with this over the years and have never had a problem.

So its best to experiment and discover such things through personal experience.

robert