First off, I do not feel sorry for Gatlin at all. His first suspension I give him some slack for as he was taking a relatively common medication, while in college, but never-the-less it was still considered doping.
Then he gets caught again, when at the time he was the best sprinter in the world, so he gets a ban, serves his time. End of story right? Yes and No. I fully believe in serving your time, and so in my eyes he is given a relatively clean slate, just like Michael Vick in the NFL and others.
However, just because he can once again compete in IAFF competition, does not mean that private leagues, and meetings have to let him compete. In fact, the diamond league (may have still been golden league at the time), held a meeting several years ago, and agreed to not let convicted dopers into their meets in an effort to improve the image of the sport. Most major shoe companies were also at these meetings and most agreed not to re-sign/sign any convicted dopers. The hope, without main stream support, these dopers would no longer be able to afford to compete and would slide out of fans' memories. The one major shoe company to not agree? Well let's just say they were started in 1972 and currently reside in the PACNW.
So moving forward, everything seemed pretty well set to clean up the sport, but then a couple of Diamond League meets let Gatlin compete. There were others too, so I will not pin this on him. Gatlin was running well, but by no means the best in the world or even his country. He was supported by a no-name company, and so he flew somewhat under the radar.
Then he started to get better, to win races, to take scalps and people started to take notice. It was okay however, because he seemed to be on a normal trajectory, and times while fast were not unrealistic. It seemed to be a real success story of a second chance taken full advantage of.
But then, he runs his fastest time ever. Faster than he did when he was doping. Faster than he did when he was younger, than when he was in his "prime". Now people really started to take notice and wonder what if. Finally a meeting said no.
Did he serve his time? Yes, should he be innocent until proven guilty? That I am not so sure about, I think you give up that right once you've been found guilty and in his case - twice.
Even if I buy the injury claim, I am still okay with the meeting saying no. They are in the business of putting on a show, and providing the best entertainment and no one wants to see an injured athlete on the track. If American Pharaoh takes a major injury this week in training (really hope that does not happen) would we want to see him trot around at Belmont (perhaps a bad example since he has a shot at the triple crown). If Demarco Murray gets injured in training camp, should he start at RB for the eagles week 1 in place of a healthy RB that would be more effective?
TL; DR Gatlin does not pass the eye test right now, and a meet promoter may have just defaulted to a previous agreement from several years ago. He may be banned from many other meets moving forward.