Certain personality traits prefer different professions.

While someone could completely have the opposite personality profile than is typical for his or her profession, in general knowing what kind of person typically chooses that profession is helpful in knowing how to (or whether to) deal with them.

People who want to be in charge often gravitate towards positions of authority.

People who like weapons also like authority in general.

People who have difficulty succeeding in something more intellectually challenging but are in decent shape physically, and want a position of authority, don't have a lot of other options. There is also the army but when you start you don't get to have authority over anyone.

This typical person is not necessarily stupid, but generally not brilliant either. Not necessarily in great shape, but they find it easier to prepare to complete physical tests than academic tests. They are more likely male, and were probably never very popular in high school, though probably not completely outcast either. In high school, they had no power. Now, they have some power.

AND BOY ARE THEY GOING TO USE IT, ANY CHANCE THEY GET.

If they think the situation will let them get away with lecturing you as if you were a little child, frankly, they're very inclined to do so. They really enjoy this part of the job. It beats the big part of the job that is just sitting around, and it beats the part of the job where they might die at any moment too. This is the authority they signed up for. Sure, it's not as good as pinning someone who's been identified as the evil criminal down and putting cuffs on them while making smart-Alec remarks, but opportunities like that are very rare. Opportunities for egotistical lecturing are much more plentiful.

DO NOT DENY THE VERY THING A PERSON ENJOYS ABOUT THEIR JOB AND THEN EXPECT THAT THEY'LL DO THE OTHER PART OF THEIR JOB WELL - You know, the part that helps you, but that isn't particularly fun at all.

Therefore, when encountering a cop, get ready for some finger-wagging lecturing, and put your patient hat on. If you can, try to use a sincere voice to either thank them or agree with whatever it is they are saying about how you did bad.

After they are done their favorite part of the job, a lot of cops will bend over backwards to help you if you're a victim. They kinda like being a hero too. Most will at least make some attempt. Of course there are thoroughly corrupt cops but they are the minority.

It sucks that most cops are insecure, but that's life. I do think it's better than no cops at all.