Yes yes, language changes over time. I've heard that mantra for decades and I know it. That doesn't mean there aren't language changes that aren't grating when they become fashionable (and hopefully temporary).
For me, "morals" being used as a crude catch-all application of "morality," "ethics," "integrity" or related concepts bothers me. Sentence example: "Maybe if society had morals there wouldn't be so many minorities in prison." 
An even more annoying otherwise-fluent-speaker modification I see is when "conscious" is used to mean "consciousness" and "conscience" interchangeably. Sentence example: "Single mothers on welfare that steal baby formula have no conscious." It sounds like they're saying the shoplifter is not mentally aware of their own actions, not that they're lacking sufficient "morals" to let their baby starve for the sake of Rules-Based Order(tm).
There's others, but those two come up enough recently, with sufficient newness, for me to bring them up here. Some old classic language quirks are so established and entrenched that even though I hate them, bringing them up would likely invite some hatemail and maybe some mystery alt accounts also sending hatemail after that. You know, because they "could care less(sic)" about what I think. 
Chauncer and Shakespeare use singular they, while the push for gender neutral "he" was much later, in the 1700s and 1800s. So from this view singular they is descriptive of how language has been used for hundreds of years, while arguing that it's a mistake or wrong would be prescriptive. And this is just anecdotal, but everyone where I live uses singular they (at least for unspecified gender people), even my grandma who uses old words and has heated elder moments.
But even if singular they usage was brand new, I wouldn't consider advocacy as a form of prescriptivism. Prescriptivism usually comes from places of authority over language, like education and publishing, and states what's right and wrong to use. I don't see he-or-she being defined as incorrect by advocates of singular they, just clunky and exclusive. Not so much "this is wrong" as "we can do better than that". An appeal for niceness and understanding, rather than an accusation of improper language.
People stop using words and phrases all the time, both intentionally or just picked up from their environment. Some words become offensive and others become disused, leading to them falling out of favor, and new words are coined all the time, sometimes as direct replacements. Just the inevitable evolution of language.
Wikipedia does state that it may include politically correct language under the label, but I don't normally see that used in linguistic discussions in my experience. I would be hesitant to include that under it, since it seems to kinda stretch the definition to the point of not-super-usefulness where asking someone to stop saying slurs or correcting your name could be seen as prescriptivism. But of course, language is determined by its speakers, so if you would include those under it go ahead.
Sorry that was pretty rambly, but basically I don't think its prescriptivist to ask someone to change their language to not hurt others.