...it's wrong for detractors of gay rights to use the "slippery slope" argument to claim that if gay rights were established then, logically, "nothing" would be off-limits.

Limits will and should be set, but within reason. In other words, things that violated the consent of another person would indeed remain off-limits for all times. The thing is, as much as gays play the game of these hate-mongers by vehemently insisting that their situation has absolutely no parallel to that of the MAA and youth communities, the fact remains, reasonable limits will be drawn at any type of activity that does not honor consent, and which it can be scientifically proven that harm would be likely to result (not simply 'remotely possible,' because almost anything is at least remotely possible).

And one thing these detractors always willfully overlook--and do not care to take into consideration--is that there is no more scientific validation for the pervasive societal belief that intergenerational romance is intrinsically harmful to the younger partner than there is for participants in same gender liaisons that are likewise mutually consensual.

Offending the sensibilities of the majority of society, or going against established societal norms, or based purely on issues related to moralism, should not be seen to constitute any "harm" to people, as opposed to ideas and concepts.