Actually, we all seem to see eye to eye on the very end of IT FOLLOWS. It's those who outright dislike the movie who look at it as a simple stalk and kill horror flick.
My issue with the last act of the movie is that it simply isn't as strong, nor as powerful as the first 2/3. Compare IT FOLLOWS to its acknowledged 'inspirations' (if this were music, this would be more of a slam dunk case than 'Blurred Lines'!), it comes up short:

While it evokes the Body Horror of Cronenberg and creates a certain quesiness, it never punches you in the gut the way the best of the Canadian Director's work does.

The ending has a nice grace note, but it never really tackles the morality of passing on the 'disease' to another person in any strong way, as the ending of RINGU did. Or, the way in which the townsfolk in the first NIGHTMARE ON ELM STREET shared culpability for what happened to create Freddy.

And, on a simple elemental level, Carpenter's HALLOWEEN has a drive and momentum that IT FOLLOWS' last act doesn't come close to re-creating. Obviously, Michael Myers doesn't have nearly the symbolic value as the 'disease' does in the newer movie, but, as a 'Horror Film' it picks up the tension as it goes along. IT FOLLOWS slacks as it stumbles towards it's conclusion. Part of it, is that there is a certain inevitability to how it will 'conclude', yet Director David R. Mitchell tries hard to follow the template of a typical 'horror ending', complete with the big pool 'climax'. (but, the savvy viewer should know that it's all much ado about very little). It also makes the (seemingly certain) idea of a sequel even more pointless than usual: It Follows Again? It Follows Yet Again? It's Still Following?

Like I originally wrote, IT FOLLOWS is a major cut above the usual horror flick. Go see it if you are into the genre.