It works the other way too,
Uke sleeps around? HE'S A SLUT
Seme sleeps around? Eh? What's new? He's hot anyway
Well, a guy's butthole is precious y'know. Other people and not the seme would get to see the facial expressions the uke makes during sex, so it would be very sad. Haha, well that's my problem in most cases. But who cares, it's fictional anyway.
I also freaking hate it if the seme sleeps around too. Why can't a guy control his dick.
Uke sleeps with another man? ''Well, it's not a big deal, him and the seme were not dating, it's the seme's fault of course, as always. I'm so happy he had a happy ending with the seme, he deserved it''
Seme sleeps with another man? In the rare cases that it happens, well kill the bastard, he doesn't deserve the perfect uke, he deserves to be executed''
Average yaoi manga reader logic.