ive definitely seen this happen, and its terrible. theres absolutely a misogyny and a transphobia problem in the gay community.
however, i dont know if that makes the assessment that cishet women fetishise m/m relationships in fandom spaces, often in BL, wrong or in itself misogynistic.
the superlatives attached are though - "all BL is written by and for straight women." "all mslash shipping is by and for straight women." (ill admit, ive probably said things like this in the past, but ive grown. accountability innit) theyre also reductive and homophobic, erasing the mlm communities within fandom spaces, and in fact the wlw who consume and produce mslash in solidarity, (and due to a myriad of other things to do w misogyny and internalised homophobia but thats not relevant)
but to say that its an issue i think is fair. the misogyny and transphobia that evolve from that statement are the doing of misogynists and transphobes, and should be addressed directly, rather than addressing the statement at large.
i guess an issue i take with your statement wrt this being an issue of misogyny is that the women being called out for this originally are cis, straight women who are genuinely cis and straight, and too often do privileged women find ways to deflect from criticism with accusations of misogyny. as a lesbian, i experience cishet womens free pass on homophobia acutely - a great deal of the cishet women who fetishise m/m relationships are outwardly lesbophobic, and i think this is part of the conversation that should be acknowledged. the straight women people take issue with in BL and mslash spaces are often outwardly homophobic despite their interests. so yes, while people should be checking their misogyny (cant believe im using 'check your __' in 2017 but it fits the context) when talking about this, it should be made clear that cishet women are perfectly capable of being the ones at fault.
that said, i do recognise that this argument can be taken further by misogynists to accuse sga and trans women of the same behaviour, which i have seen happen, and that is certainly misogynistic. i also recognise that a great deal of people who believe theyre cishet women come to the LGBT community through mslash in fandom and through BL (i was one of them.) so i agree with you that the issue requires a great deal of nuance.
you brought up lesbian porn at one point, and i believe that in this situation the flaw with your argument is that these discussions hold no place to criticise the lesbian porn industry. elsewhere, lgbt people (mainly women, lbr) are criticising that issue extensively, but it doesnt come in to a discussion about BL. i think, in fact, i would be offended if someone compared them - while it is the same process at play in essence, lesbian porn and the fetishisation of lesbians is far more institutional and materially dangerous than yaoi fangirls.
that all said, i agree there is misogyny at play in the sheer focus on that element of the issue. the stereotype of the nerdy teenage girl is a very easy scapegoat, and its difficult to separate our criticisms of straight women's homophobia from our misogyny (and in this situation, ageism as well). so... i agree with you, and i dont? but mainly i agree with you.
i didnt mention the transphobia thing that much because honestly, like, its not my place and i agree with you that its a major issue so theres less to say.