That's not really heterophobia. This is a site that predominantly caters to yuri fans.
Besides, that's not even a thing in the first place.
I dunno.... have some survey or statistical data on that?
Please tell us how many straight people are beaten to death on the streets because they're straight. Or how many straight kids are kicked out by their parents because they're straight. Or how many of them have their rights denied because they're straight. If you want to call people saying hetshit "heterophobia", you either know nothing about straight people or about homophobia.
Oppression is not an olympic sport; saying bisexuals and ace/aro who have only had relationships with the opposite sex, or even lesbians who "pander to the male gaze", aren't LGBT+ is legitimately bad for the community even if it falls under the umbrella of heterophobia. Legitimate grievances aren't negated by other people having greater concern, especially when those concerns while certainly more obviously important are far more abstracted from this forum than people being routinely shitty on the same forum is. Not that saying something is 'hetshit' is the best example of this on the forum, but there have been plenty of instances of people insisting yuri works are secretly het and stealing space from lesbians that such sentiment should be taken more seriously.