Good points. NYRR and some local marathons already have some such anti-doper policies, such as not inviting previously banned dopers, or athletes from teams with 2 or more dopers.
Apparently neither USATF nor the IOC can do that, but if convicted dopers like Houlihan could only race in official championships, the deterrent may be substantially larger.
Also people can already get their bans reduced all the way to 0 for unintentional doping, see e.g. Barber and Lawson and Wilson (and Roberts etc). Those examples also demonstrate that the doper does not even have to prove it was unintentional - the authorities just have to get convinced that it was likely unintentional. So the exceptions are already in the WADA code; all one would need to do is to extend the default ban from 4 years to maybe 10 years (to make it tougher while avoiding the lifetime ban).
