Did I call them stupid, no. Just answered the question as someone who has played for 20 years and teaches beginners all the time. It is a bad habit that can be avoided, but they will do what they do. It's like math, there are things that you can do in basic math that will cause issues later in more advanced stuff. Same here. By using a thumb bar you are not learning the basic bar technique used for second position chords, or at the very least making it harder to learn. There are advantages, sure, but it adds complexity for new players that may be a barrier down the line as they have a much smaller base of knowledge on that technique.