Unfortunately steam also limits library usage to one person at a time. For those with hundreds of games, this is very limiting nowdays if you have a family. I switched to GoG whenever possible.
The workaround is, indeed, pull the cable or firewall steam, go offline, plug the cable.
So the concern becomes "what if the protection becomes stronger".
I think Valve's definition of a family is one guy who owns a whole bunch of different computers that he wants to flit between. Maybe this is what family is to a Valve employee? I don't know.
Most streaming services allow a small but reasonable number of concurrent connections. Usually around 5. Why does Valve insist on locking out my library of games that I paid for when one person has a game open? It makes no sense.
I wouldn't complain if the rule was you couldn't have more than one copy of a particular game open (maybe have an option to buy multiple copies for the library?), but if someone is playing L4D2 they shouldn't lock someone else out of playing HalfLife 2.