No-one is saying it is...
Missing the point, mate.
I think you're seriously missing the point.
The issue is not Hawkeye's family! The issues are
a) it's not plot relevant,
b) it came out with no development,
c) everyone's okay with that. YOU are okay with that. And yet the second anyone mentions LGBT+ characters all we hear from the peanut gallery is "but is it really plot relevant?" or "it has to be organic, if it's going to be done". It's hypocritical. It's a double standard. Period. THAT is why Hawkeye's family is the Holy Grail of proof about how this works, and how clear the double standard is... because EVERYONE'S OKAY with Hawkeye's family.
Valkyrie, Loki, Korg... it's not like the MCU didn't have LGBT+ characters in them, it's just they never said they were LGBT+. But random American soldier pings his sexuality and it's TOTALLY fine.
I really do mean this constructively... ask yourself this: "if I'm using the very same arguements bigots use
(those were your words, not mine)... should maybe I take a second and think about that?"
Not on film they haven't, and that's where it counts (comics and books aren't the same thing). Harry Potter is the same (in books too actually, hilariously considering JK Rowling is "an ally" -- which she totally isn't, by the way -- side note). Star Trek was until very recently. MCU too.
a) if you are attracted to a woman not knowing it's your sister, then find out it's your sister and THEN kiss her passionately; the excuse "but when I first felt that attraction I didn't know" wouldn't work, would it?
b) Niece is still icky! COME ON! Can you not see that? It's pretty incestuous. They needed to put a pin through it ASAP; the moment he found out that should have been it over. The fact he goes back to Peggy makes it ten times worse.