I'll just say I wish more races would post discouraging remarks on Facebook. I'm a big fan of the 10k. 10k's discourage more Hobby Walkers from entering. The 5k is just a bad distance. It is short enough to allow the physically unfit and the mentally inept to make poor decisions. Many of them do not have the decency to line up where they should. Maybe it is to far to walk to the back? I don't know.
The Turkey Trot I ran had ten kids under ten years of age on the starting line. How their parents do not get charge with child endangerment is beyond me. How the race director allowed it is a mystery too. I started with a group of 3 respectfully in the middle of the race. I had to give out a warning because we would be passing 3/4ths of the people ahead of us but only 1/10 of the people behind us would pass us. I figured it was a good spot to start.
The gun went off and before we even got to the start a little girl all of three and a half feet tall and maybe 45 pounds gets spilled on the course. Luckily for her the 250 pound guy she ran in front of with his equally large wife picked her up. They may have saved that girls life with the 1,000 people behind them trying to jockey for position while chatting with friends.
As for the PC crowd. Well I agree, It is not nice to be rude sometimes it may be needed though. Someone mentioned corrals. Corrals only work if the physically unfit and the mentally inept follow the signs. The 5k encourages these two groups to join. Some people feel accomplished for their sub 60 5k's. Corrals work in marathons and half-marathons because the entries have had to put in a level of investment to even enter them. With this investment people consciously make an effort to get in where they fit in.
The big problem is the races are putting quantity over quality. This I doubt will ever change. Quantity over quality is also why there is probably one 10k now for every 50-100 5k races. The race directors and organizations would hate to lose out on all the extra income from the physically unfit and mentally inept.