I think it's just largely perception amongst the anti-systemd crowd. Systemd is a virtually unmitigated boon to Linux, but some people fear its relatively tight coupling and lack of adherence to some platonic ideal of the "Unix Philosophy". Indeed, systemd's design is inherently epicurean; the aim is to create a unified base system for Linux that reduces friction and makes people's lives easier.

"Turning Linux into Windows" is hyperbole, though; the most used and developed-on non-mobile Unix -- Mac OS X -- is similarly epicurean, and blithely makes use of tightly coupled components designed to work together, to deliver a smooth easy-to-manage experience. And it's eating Linux's lunch.