It must be young mechanics you are speaking to that are too dumb to know how to change tube required tires. There is nothing dangerous about 3 piece wheels if they are still in good shape.

http://www.accuridecorp.com/files/2012/10/Accuride-Wheels-Product-Catalog-Summer-2011.pdf

If you look at page 22 of the Accuride catalog, they still build a 3 piece wheel. If they were as dangerous as the fools you are talking to are telling you, Accuride wouldn't build them any more.