For some reason I don't understand, they're allowed to use most bike paths. That means they overtake the bicycles (and I don't like being overtaken with little clearance by larger, heavier vehicles) and leave a trail of fumes all along the cycle path. They're naturally going to be first in line at the traffic lights, spewing more fumes for the cyclists behind them.

On my commute, I'll change my route if there's a moped ahead.

(Cars are bad too, but they're not in my face, and seem to have much better emissions controls.)