fzambito:

For example: Can we now start using mentally incompetent adults for lab experiments?

No.

fzambito:

Or keep them locked up because they could fly into a fit of rage at any given moment and harm other people.

A mentally incompetent person who has demonstrated that he or she is a danger to other people should be locked up.

fzambito:

Maybe we should keep some tranquilizers on hand whenever mentally incompetent adults or children are around in case something goes wrong.

We often do drug people with mental issues.