If it's legal they can do very little, as it's only for a minute or two each day anyone with any sense who they complain to would in all fairness probably tell them STFU and stop complaining.
arrgghhh I can't stand sports exhausts on motorbikes! I'll never understand why people put up with the noise and inconvenience of swapping it out for MOT's and driving slowly round town incase anyone notices for the comparitvely small performance increase.
From that i'm guessing you haven't got a clue about bikes then
I've never swapped a pipe for MOT, I don't drive any slower or faster irrespective of what i'm riding or driving, it's all based on the road conditions, location, time of day and perceived risk, i'm very surprised other road users consider noise to be one of the factors that would affect driving speed
Performance wise i'd hardly describe going from 130bhp to 150bhp on something that weighs less than 180kg to be comparatively small but then again an indicated 160mph to 180mph doesn't do you much good at 70mph on a dual carriage way but the extra miles out of a tank from having optimum fuel mapping does make sense along with a more liner power and torque delivery that's not been programmed with the 'How can we get this through emissions reg's ? I know we'll retard the timing and fuel delivery at the start of the first three gears' pov.
Perhaps now while you still don't agree with sports exhausts you may at least see who some of us choose to fit them in conjunction with other modifications.
Edit: Just to make it clear i'm not saying putting a sports exhaust on a bike will instantly give it 20bhp, this was from a properly set up full system with custom dyno time, ignition advanced, standard air box with after market filter. It would have no doubt gone higher but I wanted torque not top end.