That's what happens, a few abuse the system and everybody else is penalised for their deeds.
As far as I see, as soon as one or two dishonest people abuse the system, everyone is made to pay in the UK, when it would be far fairer to catch these people. It's the old school mentality: someone writes a nasty anonymous letter to the headmaster? Simple: don't waste time and energy trying to identify the culpit, just punish all the pupils. In this case it's far more unfair in that the legitimate visitor cannot possibly get his own back on the dishonest one.
Thank Heavens that, though English, I don't live in the UK: if I did, I would never have managed to bring my fiancée over on a tourist visa and would never never have been allowed to marry her either.
We both work and none of us ever have had any recourse to public funds whatsoever now or before, neither was it a sham marriage as the UK Embassy in Rome seemed to believe.