Being a "professional" is an attitude.  

It basically requires that you will follow the law even if it is inconvenient, even if all your friends are doing it, and even when there is almost no chance of anyone ever catching you at it.   

I had to do it in virtually every 'job' I had for my entire life.  

If you can't do that you aren't really a "professional".   

And when you violate those standards, you are and should be held more accountable and receive greater punishment than a non-professional.  

It is part of your personal ethical standards.