15 years ago I was "ambivalent" on this at best. Back then I considered it a private sexual matter and as long as both adults were OK with it, I had no objections. However, at the time, I did not feel any need to elevate the discussion beyond the bedroom. I considered it private behavior and no one should be discriminated against for their private behavior as long as it was kept private.
I came, though, to understand that forcing gays people to be "private" while "straight" people we allowed to be open and demonstrative was harmful to gays. It forced them into unhealthy behaviors and unhealthy relationships (both gay and straight) that was causing these people immeasurable harm. Once I came to understand that my position, as harmless as it seemed, was harmful toward all gay people I asked the next logical question.
Is there a justification for this harm.
As harmful as prison can be I can justify putting molesters, rapists, robbers, murderers there because of the harm they cause others. I can even justify taking a person's life if the harm they are causing or the threat they pose is great enough but, what is the harm or threat gay people pose?
Well, try as I might all I could come up with was that I might be offended or made uncomfortable. That's it. Well guess what? I still don't want a gay corps marching in the St. Patrick's Day parade any more than I want a "fat guys who like to do it in the kitchen" or "mile high club" group matching in the parade.
There's a time and place for everything and the time for a gay couple to hold hands or kiss goodbye or get a big hug is the same as it is for any straight couple.
The dungpile that people being gay, gays getting married, gays having equal marital rights, gays adopting and whatever needs to be shoveled into the crap wagon.
In the interest of full disclosure:
While I would oppose a gay group or "fat women who like to be on top" or other similar groups marching in the St. Patrick's Day parade I could easily be convinced to allow a group made up of Victoria's secret models, Playboy Bunnies, and Hooters Girls to march in the parade because I am, after all, a pig at heart.