It impunes their intelligence because there was no rational reason (i.e. evidence) that it either worked, or that there was a problem in the first place, and the result of the operation is a bloody big hole in your head and quite possibly death through blood loss or infection.

The majority of people in developed countries are definitely more intelligent than they were historically. Genetically it is disputable, but the intelligence which we learn, and the intelligent approaches we have learned as a society (for example skepticism) have clearly improved over time historically.

I.Q. tests also show a constant rise since their implementation (to the present day). Some say that's due to more visual environments, but whatever the reason, the increase is extremely apparent.