Without getting into the debate about good versus bad and which side is which, I don't quite understand why so many police departments feel the need to use SWAT on every run of the mill warrant. Just from an officer safety perspective it seems like it would make more sense to wait outside quietly until the subject of the warrant comes out. I mean, unless you do something to spook him, he's probably going to come out every day, right? Arresting him outside seems safer for both officers and citizens.
Running into a house with weapons is obviously going to provoke some homeowners to defend themselves - why wouldn't you just wait until he comes outside? For that matter, even if you want to knock on the door and tell him you are there to arrest him you'll still get him to come out more often than not - you may have to wait six hours to do it in some cases, but I bet you'd save a lot of police and citizen's lives by doing it that way.
ETA, I base my statement of "every run of the mill warrant" on watching reality TV shows like Dallas SWAT where they go after everyone with a drug warrant like they are expecting to find an army on the other side of the door.