I agree with you Andy, but I would go a bit further and say it really doesn't matter to me at all whatever is going on with other riders and whether they are cheating or not, as long as I enjoy the race and get a good workout.
There's literally nothing at stake except my own fitness. If one of the riders I'm racing against online is doing something to boost their performance and is in reality a much slower rider....so what?! If he gives me a good race within the game, that's fine with me. And if he wants to kid himself that he's a better rider than he is in reality, again good luck to him - I couldn't care less! I'm either never going to meet them anyway, or if I did meet them IRL and they were shown to be way slower than their online racing suggests, that's their problem not mine! Or, as a user of an "unfair trainer", it might be more accurate to say my problem not yours
P.S. That said, big difference between cheating by fiddling your weight for example vs just happening to use a trainer that is inaccurate to the extent it gives an unfair advantage - not really much people can do about the latter!