Smoker here, and yeah I have asthma, which as you can imagine isn't well managed. I wear a mask. Sometimes I need to take a break from it for a few seconds (and I really do mean 5 seconds or less) at a time, and no, I'm not immediately reaching for the fags.
I have a colleague with mild, well controlled asthma, non-smoker, who claimed exemption (then starting wearing one because they became worried about CATCHING covid, not spreading).
I think YABU to ask this question at all. Plenty of non-smokers taking the piss with the exemption, to be worked up about asthma sufferers who smoke.
BTW asthma symptoms vary throughout the day, so it depends how well managed their asthma is, when it's at it's worst, what triggers it.
Smoking whilst you have asthma isn't healthy, and sufferers are aware of that. Yes we worry about it, and worry about what will happen if we contract covid. Yes we have awful self control and can't just put the fags down. Happy now? Or want to do some more smoker-hating?