Once upon a time, it was difficult or impossible to attain certain skills without committing acts which might have been ambiguous then, but are now clearly "breaking the law".

It's all different today, but Mitnick is old school.

The rest of the security company founders who were active in that era but do not have felony records...by and large, they just didn't get caught.

Which sounds like it might be a reasonable criterion for judging skill, but the scene was so tight and inbred back then that getting caught often had more to do with who your friends (or enemies) were, than with your own skills.