I don't hate the leagues, although I also don't play on them anymore because there are no more left in my area with challenging players in them.
However, I do have three big beefs with the league systems, and I say this with the understanding that operators and such are doing their utmost on the whole to combat these things.
1. The culture of sandbagging to get an advantage. We all know there are very, very, very few saints among us in the pool world. That being said, I've watched this happen on every team I've played against, and on my own team. One of the reasons I quit playing league in the first place was a co-captain who kept asking me to lose games because my handicap was getting to high. It just got to the point where you were never sure you were getting an honest game anymore, and that irks me.
2. People who don't read the rule book. I get that league is a place to have fun and not necessarily take pool too seriously. Yet we've all seen this person at least once. The ones who don't understand you can use your cue stick to move the cue ball on a ball in hand as long as the ferrule and/or tip don't make contact. The ones who call a foul when you hit a frozen ball first and then a rail after contact. The ones who don't understand that on a scratch on an 8 ball break it goes behind the headstring, not ball in hand. The list goes on. I'm also not very fond of the opposite folks, who seem to call a foul on every single shot whether there was a foul or not. Both these types of players drain all the fun out of the game when I play them.
3. People who think because they are a 6 or a 7 in the league they can go toe to toe with any pro. This right here is admittedly just a personal preference. I'm nowhere near pro caliber play, but I'm not half bad either. I've shot a few racks with people like Ralph Souquet and Karl Boyes. I've actually drawn Mike Davis for a tournament a time or two in the greater area. Most leaguers, even the 8s and 9s, are not on the same planet as those guys. So it bugs me when someone cops an attitude like just because they are the best in a pool of folks who are just out to have fun like they are the best on earth. I get being confident in yourself, but have at least a little humility and perspective.