[Jtsummers]

Something similar could've been said about both interracial and same-sex marriage.

If the relationship type (interracial, same-sex, poly) is considered in some manner deviant or otherwise unacceptable, the number of people openly engaging in it will be small. As race relations in the US improved, as attitudes on same-sex relationships improved, the number of people openly engaged in these relationship types increased.

As poly relationships become more acceptable, more people will admit to being in them. Then we can examine what percentage is impacted by not being able to marry.