That is the whole point of the doorways.  To canalize people. 

Block and FF works on larger servers.  [Q] aka [SiX] always had them and were full, but the owner had to shut them down.  CSG back in the day(2004-5) was no block/FF on.  Mercnet(2007) was a 40ppl Block/FF on server always full and I was an admin there. 

All you had to do was the occasional spam of Intentional Teamkilling isn't tolerated or Stop Blocking.  Problem was solved. 

Occasionally, people spwn in each other on inferno and a few other maps, which an admin just has to smack them or teleport them.  If not, humor in that round for the two butt buddies.

Humor was added from the killing plugin.  Douchey players were banned for blocking doorways.