The similarity would extend so far as the negative views society has for people in any of those groups. In all cases members of society currently hold or have held in the past a view that these behaviors even when not having a negative effect on any individual are something which 'erode the moral fabric of society'. It is not a similarity in the groups themselves, but in how they are regarded or have been regarded by others. Forcing ones morals upon others in instances where there is no harm to anyone(while arguable in many cases of cheating, is certainly true in some cases), would be the common thread.

For everyone who identifies as some sort of Poly or other group it is probably painful to have members of other groups, which are unfortunately still discriminated against, view their differences from the accepted moral norm in a negative light like this. People in general want to be accepted for who they are, and ideally judged by a moral code similar to the one they themselves hold.

At least that is my view on the situation. I realize cheating is often not a mutual agreement between all parties, and in those cases a person is being harmed and there is reason for society to view it negatively, however that is not always the situation, and in these cases I think other groups who have been discriminated against recognizing the similarity would be valuable to humanity in general.