Debian's policy is that if you install a service, you intend for it to run by default. Since services aren't installed by default, this is a fairly defensible position, though it's been commented on many times.

It's possible and fairly straightforward to disable autostart of services through either old-school SysV init or, I suspect, systemd.

Upshot: running complex systems isn't entirely trivial.

Yes, a desktop computer is a complex system, that's why I leave these not entirely trivial plumbings to the system programmers. The downside of this is the exploited systems that potentially everyone has to suffer.

This story doesn't check out; I don't see a package named "openssh" (on Jessie), but there is a package "openssh-client" which only installs the client.

But regardless, starting sshd on installation shouldn't matter because proper passwords and firewall should be the first step.

Welp, the metapackage's just called ssh, which is also the name of the command the client provides. Another case of "only two problems in computer science ..."

Due diligence on my part was lacking, agreed.