There is no way to answer this question factually -- it is simply a matter of opinion and one person's opinion is as good as any other person's.
My opinion is that it makes some sense for us to help stop doping in other countries if only because we want our athletes to compete on a "level playing field." If our athletes are not doping (that might be a big if) then we do not want them to have to compete against athletes who are doping and are, presumably, getting a competitive advantage.
So I think that we should help contribute to international efforts to stop doping (like the WADA) so that everyone can compete on an equal basis.
I find it difficult to find a reason why the United States should not take an active role in eliminating doping in other nations. If the notion of international gaming is brought into question because of doping, the United States and other nations have an ethical and sportsmanship responsibility to act in their power to eliminate doping. It taints the sport to have a spectre of doping around competition. I think that if the United States can help to take a leading role in eliminating doping in international competition, it might help to spur on change so that there could be a legitimate and thorough policy in domestic sports to eliminate the use of performance enhancing drugs. If the United States can take the backwards role of leading the world, it might be able to provide the same level of change on a domestic level.