From where I sit, the opposition is from people who don't like, approve or trust how systemd is incorporating more and more into itself. It smacks some people of bad design, bloated design and insecure design. Plus, it's the kind of behavior most often seen and witnessed by the historical enemies of Linux; it's the method of feature creep that reminds people of Microsoft and others, designed to make it difficult, if not impossible, to use anything else... ("lock-in" by another name). I'm sure that much of the "small elite" in opposition are opposed because Linux was supposed to be the revolution that got us *away* from that sort of monolithic control that they see systemd as.
As for me? meh.