milk runners simply take an undefended field because they can't deal with taking one that's defended. The second even one defender shows up they scatter, run, and go to the next farthest-withdrawn field they can get to and try again there.
If, however, there is a very large horde-on-horde clash going on in one sector over one field, and a group of folks set up a mission to take a field 2 sectors down, but still on the front line, they will draw a large number of that horde off.
Basically griefers and milk runners don't help anybody but themselves. Like the folks that launch missions to go 5 sectors behind enemy lines to take the 163 base in sneak attacks, and the like (and yes, I remember at least one time when folks tried to do this mission, but I think they failed).
I'm willing to give the new base capture a shot, if it reduces that aspect of AH gameplay.