The prerequisite for discrimination is simply being different from the majority of the society! not being normal!
So what makes you think, in an over-sexualized over-romanticized world, where sexual and romantic relationships are THE normal, an asexual and/or aromantic person is not discriminated?!
I've been feeling wrong, diseased and broken, casted as an outsider, alienated, ridiculed, humiliated, hated, pitied, and treated like less than what a human supposed to be like all my life, before and after I found out my orientation. I call myself queer and believe I'm part of LGBT community because my experience has been very close to my gay/bi/pan friends and very different from my straight friends.
The confusion, the questioning, the fear, the Am-I-queer online tests, the loneliness, and therefore the need to find people who have similar experiences to me, the need for a mentor, the need for validation, the shame I went through because of my orientation, the oscar winning performance of acting straight because I wanted to fit in, the straight romance model in media I couldn't relate to, not completely at least, the pressure to pursue a romantic sexual "normal" relationship when it didn't feel right, these are all the things I've been dealing with growing up.
So if a friend comes out to me as gay I'm gonna respond with 'I know because I've been there, here's a safe space for you to be who you are. I got you'. Because I do. Because no matter what gatekeepers and aphobes think, I've actually been there and I know what it's like.
If the mental trauma a queer person goes through is not valid enough for you to be counted as discrimination, you need to recheck your beliefs.