Hmmmmm...interesting question. Obviously it is not going to happen overnight, and there is no way to win over EVERYONE. I am thinking that we need to stop showcasing 6 year old black belts (for that matter, say something to anyone you know who has a school that HAS a six year old black belt). (We need to) Stop claiming that TKD is several thousand years old. It is about 50, with some skills that may date back thousands of years. Stop trying to tie TKD to Taekyon, Hwarang, etc. It is okay that we can state they have influenced the 'flavor' of TKD, but seriously, drop that line of bull.
If TKD wants to be taken seriously (as a martial art) we need to show its combat effectiveness (and in some schools, learn combat effectiveness). If TKD wants to be taken seriously as a sport, we need some sort of pro-league, because lets face it, TV time once every 4 years at the olympics is pretty pathetic. Heck, poker is not even a sport and it is on multiple times a week!
Just a few thoughts. If I come up with more or a better plan, I will share more, if not, well, there you have it!