Unfortunately, things aren't as simple as you'd like them to be.
The systemd developers have made many political decisions that ended up putting systemd in a position that makes it difficult to avoid. The prime move often cited is the engulfment of udev inside the systemd codebase and entangling it with systemd's shared files (formerly belonging to libsystemd-shared, not it's just a big libsystemd blob), and later rewriting the build system so that it was harder (though not impossible) to make udev-only builds. This and many other decisions prompted the creation of eudev. Of course, now they're converting the transport layer from Netlink to sd-bus, thus intending on making udev systemd-only, and taunting Gentoo users along the way.
Furthermore, various distribution maintainers (though particularly Debian and Arch) are placing various components that optionally use systemd libraries, or provide systemd units, as being dependent on systemd. You can see this with Arch and lighttpd.
Further, GNOME's adoption of systemd libraries was negotiated by Lennart as far back as 2011. Though it would have likely occurred anyway, he was an active instigator in the ordeal (https://mail.gnome.org/archives/desktop-devel-list/2011-May/...), and a couple of years later was arguing on his G+ feed that with systemd-logind being unportable and inseparable, that this should be a reason for Debian to adopt it. He chose to do this rather than continue ConsoleKit or make logind an independent daemon. Currently, more is being consolidated: Avahi is now becoming systemd-resolved, and kmscon is becoming systemd-consoled. Among other examples.
But it's not just the GNOME Shell, some core Desktop Linux applications now depend on systemd libraries, as well. upower and udisks2 come to mind. The former even caused quite a stir in Gentoo circles when a regular upower update was suddenly pulling in the entire systemd stack.
The whole point of systemd is to be the standard userspace middleware for a GNU/Linux system, and to be an absolute essential.
No, Lennart is not a rampaging monster, but to say that he's just some innocent bloke who's simply releasing free software, is bullshit.