I used to think I was a pretty good shooter... Then I started competing. It really can be eye-opening.
A lot of people can't take the ego hit that occurs in their first competition, so they go away, never come back, and then (often) start repeating the mantra "that stuff will get you killed on the street" so that they don't have to ever be compared to good shooters again.
Everyone who says that isn't in that category, of course. However, if you hear someone say it---either they haven't tried it, or just weren't very good. Or maybe they believe it, because they haven't thought about it very much.
Let's see: Mike Seeklander, Kyle Lamb, Frank Proctor, Bill Rogers, Pat MacNamara, Shannon Smith, and many others----ALL talk about the good things of competition. (Heck, Larry Vickers was one of the founders of the competition sport of IDPA. One of the scoring methods is named after him!)
Who doesn't speak well of competition? People like Rob Pincus, who maintains that his method of teaching is the best due to his huge amount of personal experience, which consists of a couple of years as a 2nd Lt in the Reserve after ROTC, a couple of years as a cop in a small town, and a few years as the director of security of a resort.
Don't get me wrong---Pincus is extremely well-known, has fantastic marketing, seriously good networking skills, and makes tons of money from his classes, DVDs, etc. He's even talked the NRA into including some of his DVDs and such with the NRA materials.
He's also the idiot talking about things he either doesn't understand or deliberately misrepresents in the first video from this link:
http://www.gunnuts.net/2013/04/11/tactical-vs-competition-theres-no-controversy/He deliberately doesn't allow any objective skills testing in his classes and won't use timers and such for measurement of improvement (so none of his students know if they can meet even basic shooting standards, and certainly can't tell if they are actually improving), and actively says that competition shooting "will get you killed."
Amazing how many people disagree. Like Bob Vogel (cop and USPSA Grandmaster), Ted Puente (cop and USPSA Grandmaster, well known for Multigun championships), and JJ Racaza (homeland security officer and USPSA/SCSA Grandmaster).
Competition shooting won't teach you self-defense tactics. It will, however, give you important feedback about your
shooting skills.