Why not?
Guys: I'm not some demented freak who rubs his hands together and laughs maniacally when I see a bug. It's not like I'm delighted by pain or that I hate all ants -- except when they get on my stuff. I have a neutral attitude toward them, but that also means I don't care about them. They're just ants and their lives make no difference to me, which means if I feel like stepping on them out of boredom, then I will.
Religion aside, what are the possible consequences of this, practically or philosophically? There are none.
Yeah man it's gross. They might stick to the bottom of your shoe and gunk up in the treads - then you've got little exoskeletons and ant guts in your house.
Think about this...viewed from the andromeda galaxy, is there a significant difference between you and even one ant? I say no. You are more significant than an ant to us because you can come on a message board and brag about how many ants you killed, while some ant survivors cannot come on here and tell of the atrocities that befell them at colony234234 in the quadrant 654266 in the life of queen 1324134.