Then they would need to stop selling perfumes (which for me personally is worse that cigarette smoke), prohibit perfumes from coming in the gate, stop selling nuts, and not show fireworks, among other things. In this world, it is pretty much impossible to make a place like WDW 100% safe for every asthmatic out there. It's the job of the asthmatic to manage his or her asthma and avoid triggers, and that includes knowing where smoking areas are and avoiding them.
Smoking areas are, for the moment, necessary. People who are smokers are going to light up. There is no way around it. If you eliminate smoking areas, then the problem of people smoking where they are not supposed to will only get worse, and the people who suffer the most from that would be asthmatics. We can avoid smoking areas. We cannot avoid people who choose to smoke where they are not supposed to, and eliminating smoking areas will only make that problem worse.
Nevertheless, the smoking area near the castle ramp was extremely poorly placed, and I am glad to see it go.