This is a rare forum on the internet in that for the most part, it's made up of members of the gun culture who actually strive to better their skills by education, training and practice with their choice of weapon.
Training is good. Training builds skill, which in turn builds confidence. But one must be careful that this confidence does not turn into arrogance.
I think that it would be extremely dangerous to assume that a criminal is less of a threat because he does not train. When you are suddenly confronted with a critical incident, how do you know which category your opponent falls into, trained or untrained? Looking at the quality of the weapon or lack there of is not an accurate representation of one's level of training. Just like when you are standing on the firing line of your favorite gun range, the guy to your left may have the newest and greatest pistol, and be in the process of shooting himself in the foot. The guy on your right may have a used S&W SD pistol he just acquired, but he also has four combat tours under his belt and knows a bit about how and when to utilize appropriate tactics.
A private citizen who is a moral and law abiding member of society may hesitate to actually put rounds into another human being. A inter-city thug who's shot people for disrespecting him in the past and the offense has gone unreported will not hesitate to pull that trigger. That second of hesitation can often negate any training the good guy may have under their belt.
How many times over the years have we seen a suspect win due to pure luck. And how many times have we buried good men because a lack there of.
When I confront a suspect on the street, I assume that they are well trained, just to err on the side of caution. When I train, I tell myself that the person I am training to confront is myself.