I don't see the difference between height discrimination and racism against black people in this context. It's like saying racism for Asians is not real racism because they don't really have it that bad, all things considered.
Nobody is arguing that being short is as bad as being black in society at large, but that's not really what the topic is about.
"No short guys", "Just my preference, plz respect it", "ugh, no fatties", "$100K+ only", or whatever things dudes put in their profiles all say unappealing things about your character. No one is saying don't have a preference, but wearing it on your sleeve as some sort of badge of honor just shows a lack of class, in general.