Bringing a gun escalates things immediately. If I was in that home and I was carrying a gun, and if a handful of people abruptly came in with assault rifles, I'm liable to react very differently because it's such an affront to what feels reasonable. I think it's more reasonable to think that this is a terrorist attack and to react accordingly, rather than the reality of people acting as an agent of the government bringing deadly force in droves because someone grabbed a file from a public FTP server.

If I had seen 5 men in suits and shades peacefully walk in without any kind of weapon, I'm not going to think anything of it. They're putting themselves at risk. It makes no sense.

And the honest answer as to, "why?" is that the people who kick in doors are complete meatheads who think that morality and legality strictly align. They think if someone has broken the law, they deserve anything that is coming. They don't care about anyone's safety, they care about taking baddies.

Now I'm not sure where their training draws the line on infant collateral damage: Don't shoot in rooms with babies? Shoot around the babies?

But imagine if the rule was: Don't upset the children. (silly I realize, but thats how what-ifs are played). It seems like decisions would be made resulting in fewer grenades landing in bassinets.