Had a really heated debate about this the other day with a "why don't they just let them take all the drugs" view holder.
My reasoning is that whether there is or is not a benefit from taking it, it's legal if you follow the correct protocol, and if there is a tiny gain to be had even though it might be unethical, then as an athlete they should take it, it's not their responsibility to make the rules. When it's legal if you follow protocol - a line in the sand is drawn. In Yates' case, he tripped over the line and crossed it, but still crossed it (I may have run with that metaphor a bit too much)
In the same way that most athletes who took Meldonium probably didn't have a heart condition, most athletes that take asthma drugs probably don't have asthma. The problem is that asthma is very much on a continuum and putting a line along that, where some are asthmatic and some aren't, is extremely hard. In the case of Yates it seems he genuinely does have asthma; if Owain Doull is a reputable source:
(how on earth do I embed tweets on here btw?)