I agree with eagles 2k3 on a very important point. It was definitely the parents who didn't play sports or who had very little experience on the field, court, ice., etc. who were, by far, the worst parents.
With that said, I don't know if it has gotten worse in the past 15 years or so. But my kids played, baseball, softball, volleyball, football and basketball in youth and HS sports with two of them going onto college to play football, baseball and softball. I haven't seen or coached in that world for at least 15 years but did from 1993 - 2010. I assume parents, in reading the posts here that nothing has changed much.
When they were little and in youth sports there were some parents who were clueless. But with our oldest the parents really weren't that bad at all. With second oldest the parents were bad on certain teams and not so bad on others. The baseball parents were clueless and bad but in basketball and football they weren't that bad.
The parents on my third oldest were bad in baseball till we took him off one team, put him on another, and those parents were pretty much the same. Basketball parents weren't that bad and the football parents were pretty good in his grade in HS. But the grade older than him had a slew of real a-holes. Glad when their kids, and they moved on.
The youngest had pretty good parents for basketball and volleyball. Softball parents were good till that one got to be 10 and we put that one on another team. Those parents were ridiculous at times. Saw a couple fights in those years.
But I just remembered when my second oldest was playing baseball, that one was on an 8 year old "all star" team. We were playing against the Morris 8 year old team. The coach on that team took a kid off the field in the middle of an inning because the kid made a couple errors. Soon after I could see the kid's dad saying something to the coach through the fence of the bench. After the game we saw those two arguing from across the parking lot. The dad of the kid pulled a gun on the coach. He didn't pull the trigger, but I stopped in my tracks and was wondering, WTF!
Overall on a scale of 1 - 10 with 10 being the best, I would say the parents were maybe five and a half or six. There were a few who were terrible, but nowhere near the majority.