Opening doors is one trick I definitely wouldn't teach pets!
Many years ago my parents' cat started trying to open doors without any training from us. She clearly understood the process from her efforts, but couldn't grip the round handles. Given a house with cranked handles though and any door that opened out rather than in would have been insecure to her.
Oh, her house is out in the garden so she only has access to the garden door, all the other doors have keys and she hasn't managed to grow opposable thumbs yet, so I think we're safe :P I do agree with you for house pets, though.
Many years ago my parents' cat started trying to open doors without any training from us. She clearly understood the process from her efforts, but couldn't grip the round handles. Given a house with cranked handles though and any door that opened out rather than in would have been insecure to her.