The most interesting opinion about this subject I've read comes from a comment, in the popehat blog, by an experienced military:
There is plenty of reason to restrict the use of SWAT teams, but not to abolish
them. They are needed now and then, when there is an actual hostage situation or
an armed gang that tries to shoot it's way out. They should never be used for
routine search or arrest warrants. That not only endangers the possibly innocent
target of the raid, but it undermines the team's training – they become used to
tearing up houses where no one is resisting. There's a dashboard video of the
Jose Guerena raid. My drill instructor would have said they looked "like a monkey
fucking a football" – and I was in the Air Force, ground tactics weren't even on
the curriculum. I've seen considerably more forceful comments from Army and
Marine Corps infantrymen who actually have had to break into a house against
armed defenders. They milled around, exposed themselves to possible fire through
the open door, and got into each others line of fire. They did NOT identify
themselves as police that I can hear on the audio track, so Guerena was justified
in hunkering down in a defensive position with a rifle. If Guerena (a former
Marine) hadn't been far more professional than any of the cops and not fired
without identifying his targets, several cops would have been down.
Then there are the SWAT members that "accidentally" (that is, negligently) fired
a round and killed an unresisting, unarmed suspect because they tripped or
bumped their elbow – an accident that can only happen if you are in violation of
the two most important rules of gun safety: don't put your finger on the trigger
until you have decided to shoot, and don't point the muzzle near anything that
you do not intend to shoot. We know they were running around with their finger
on the trigger – in a situation where there was clearly no need for shooting –
because modern firearms in good working order just don't fire unless the trigger
is pulled. The military just doesn't tolerate that. If a non-police civilian in
my state had done this, he could have been sentenced to life for manslaughter.
But if you are a cop, you can recklessly kill someone and the prosecutor will
throw the case…