Well ideally your infantry ought to be rooting out and spotting ATGM teams /before/ they get to shoot, but that might be a little old fashioned thinking on my part
I agree that once the missile is fired its too little too late, but if the infantry are doing security properly, they can mitigate AT attacks. Again, I would rather have the infantry than not in this kind of house to house fighting, especally since they can clear a rooftop...the tank can drop the roof but it sure as heck cant peek up there itself.