While nobody would chose to be unsafe or unprofessional just because they aren't paid much, there is still a connection. A pilot who is underpaid is generally going to be more stressed at home and has a higher chance of fatigue. If you're forced to live in a crashpad or hooptie apartment with loud neighbors, you'll naturally not be at your best at work. Add to that the lower nutrition, quality of life, high debt, and any number of other side effects to not getting paid sufficiently, and you get a lower quality pilot.

People may not desire to be that way but to just dismiss that pay has nothing to do with the quality of the pilot is a short sighted view at best.

And as for the pilots not ironing their shirts or generally being unconcerned with "professionalism," its hard to be one when your company treats you like day labor. At some point it gets easy to stop caring when it seems everyone else at the company has stopped a long time ago.