While I agree that they are pointless as-is, something is off with your setup. They never spawn inside my real bases. I have one with a moat, and often have them fall in the moat and get stuck there until I have time to deal with them. I have another with tall terrain-walls that they just stand there staring at until the timer runs out then they run off. But nothing shows inside -- when it does, I try to figure out where they appeared and add a bench or something there to stop it. The radius of the bench may be slightly overstated; I had that problem on a lofted farm (raised terrain for planting wheat) where they spawned up on the cultivated dirt and wrecked my crop. A second bench put a stop to that even though the original indicated it was fully covered, there was a microscopic spot or something out of the ring or computed to allow a spawn point.