For example, there is independence day within the US. This is a day of pride and celebration for those who identify themselves as American citizens, who form the vast majority of US residents. However, there are also those who live within the US who do not identify themselves as US citizens. Mexicans, Europeans, Canadians, whatever it may. Not to be flippant, but according to your definition, this would be a celebration where the majority is expressing pride in their identity and thus, establishing superiority over the minority. However, I personally see it as a celebration that does not detract from those who identify contrary to the majority. It is one where US citizens feel pride in their identity, but a pride that does not pose a threat to others.
With this in mind, isn't it possible that a member of the majority (heterosexuals) could express pride without it posing a threat to others?
I think that the Fourth of July largely is, as it goes, a celebration of what makes us different and, by proxy, why we might prefer the United States over other countries. It doesn't mean we are threatening the others necessarily, but when you listen to the rhetoric that comes with celebrating being an American, it is always saying stuff America is like "A free country." and all that with the implication that this is a unique quality. And I do think it would be healthy if we toned down our rhetoric in general because I think nationalism leads to delusional thinking. Mind that I'm not saying the fourth should be banned, because when you strip away the rhetoric you still get a summer holiday where you blow shit up and eat barbecue with friends and family, and I'd have to be a sad fuck to poopoo those things. But if you look at patriotism and extend the same practices and assumptions to a pro-heterosexuality movement, you can see how it could get awkward.
Which I guess comes down to what you want to do. If you don't want to draw lines, say "We make babies and you don't" or whatever, then what exactly does a Hetero-pride movement achieve? If you want to meet other heteros... well, that is easy. Hopefully nobody is shaming you for your heterosexuality, in which case you wouldn't need the solidarity part of it. Is it just that you want a parade? Because there are less controversial ways to get a parade. Or do you feel left out because people from other groups are posting X-Pride and you're checking in the majority boxes all the way? Because if that is true it would be a really interesting sociological thing (I feel left out of being left out.) I dunno how you could fix that. Another hobby I guess?