like how they speed to catch speeders, shoot at people who are shooting at them or others, lie to get the truth from liers, etc.?
as for people "bassing" probably 95% of the people they pull over dont have a loud system or system at all. "rumblers" are used on emergency vehicles to help alert people of their presence. if you have your radio up decently loud with the windows up, its very easy to miss the ambulance until its rite behind you and you're in the way.
a big part of a cop's job is to save people. just like firefighters and EMTs. they just all do it in different ways. so whatever gets them to the scene faster, I'm all for it.
edit - by the way, this is an old ass video. these have been in use for a while.