Firstly, it wouldn’t be murder, it would be manslaughter- or, I suppose, antslaughter.
Second, ants aren’t stupid; they stay away from feet. I have noticed that it is difficult to accidentally kill an ant because they can see the shadow of one’s feet and anticipate where and when they will descend. Granted, if one is trying to kill an ant it is possible, but my point is that accidentally killing ants doesn’t happen very often, in my experience. Anyway, as you pointed out, it is only two small areas of the foot that are in danger of killing ants, not the entire area of the foot.
B’chol zot, nobody is pretending that ants have the same rights as people, but they are still God’s creatures and deserve our consideration. When I find an ant in my house, I let it crawl onto a piece of paper and take the paper outside, rather than simply killing it. (Ditto for spiders/beetles/etc.)