The difference between them being that racism and homophobia are prejudices about what someone is, while the pushback against genderism is an objection to someone claiming to be what they are not.
No one cares that trans people and their allies have an inner belief that their soul or whatever it is a really one of the opposite sex. (Well to be fair I kind of do because it's horribly sexist, but as long as they can't impose their sexist ideas about what makes someone "really" a man or a woman on the rest of us it is their right to believe it).
What people push back against is the demand that this self-reported inner soul feeling be treated as if it makes the person actually interchangable with the opposite sex in areas where physical sex (not mental self image) is considered to be significant and relevant and at times, a factor in risk or in disadvantage that needs to be recognised and mitigated.
Saying "No" to that demand is entirely different to racism or homophobia.
Indeed, I would say Genderism itself is closer to racism and homophobia in that it takes something about a person's material reality and claims this determines who they are as a person, their tastes or abilities or aptitudes.
Whereas Gender Criticism says "Since there isn't a specific type of personality that is innate to a male or female body in the first place, there cannot be the possibility of it somehow getting into the wrong body. Being female comes with material physical and social risks and consequences. Whatever trans women are experiencing it's not being "really" female, it's not experiecing life as female, and it doesn't justify opening up female language, supports, rights and protections to accomodate it.
That's all.
Sometimes, to respond to people who challenge this and claim that if a man experiences life as a "woman" enough he is at least socially more aligned to female people than male, we need to give examples of just how different some of these men who claim to believe they are women's idea/experience of "womahood" is, which is where things like AGP come in.
And sometimes, to respond to people who claim trans identities must be more than this because they are observed in young children, we need to give examples of children being - I'll avoid the G-word - strongly influenced to interpret very common childhood and adolescent feelings through a one sided and fake "scientific" gender narrative which is where concerns about children and activist overreahc in schools come in.
And sometimes, to respond to people who claim trans women could never be a risk to women, we need to talk about rapes and assaults and threats which is where screenshots like www.terfisaslur.com and people like Dana Rivers and Isla Bryson come in.
But no one is saying these things are the definition of trans women, or are true of all trans women, simply that as long as they are true of any trans women, the #bekind belief in the harmlessness and vulnerability of trans women that underpin many well meaning trans allies is sadly not true in all cases, and that following this path does do genuine social and at times even physical harm to women.