AGP is short for autogenephile, someone who has sexual fantasies involving themselves as female. There were a few things that Blanchard overlooked when he coined the term, which he later acknowledges and he stance on transsexuals has changed since then, which he greatest fans also ignore.
nearly all cis women's sex fantasies also involve themselves as female
nearly all cis men's sex fantasies involve their penis... does that make them autopenephiles?
nearly all cis men do not ever think about being female, ever. Not in sex, not in life, never ever. Women are like another species to them.
HSTS are "straight" transsexuals, for example transwomen who are interested in men. Blanchard's original works defined them as the only "real" transsexuals. Even though Blanchard himself has said that with modern research his view is more nuanced, transphobes have used
AGP
as a kind of shorthand for
I want to call you a man but I don't want the social repercussions of being transphobic
I think it's something larger in society. Everything is porn now catering towards coomers. Every piece of media, every movie, tv show, shitty tabloid for the boomers who still read those, no longer uses sex but is about sex. I don't think taboo-ness is the answer. I think that's how we got to this point.