In the wake of several high-profile incidents in the late '60s and early '70s, culminating in the massacre of Israeli athletes at the Munich Olympics, nations around the world began developing specialized military or paramilitary police forces to deal with armed, dangerous terrorist-style threats in the middle of crowded urban spaces filled with innocent bystanders.
Outfits like Germany's GSG-9 or Britain's 22nd SAS Regiment scored high profile successes in Operation Feuerzauber and Operation Nimrod, and by the opening of the 1980s, most large law enforcement agencies had units trained in storming a building to resolve a hostage crisis, from the early pioneers of LAPD SWAT to the FBI's Hostage Rescue Team. And when the LAPD and FBI sneeze, the Anytown Police Department catches a cold. Soon, pretty much any agency that issued badges had some form or another of a SWAT team.
All issues of right and wrong aside for the moment, there are a couple of colossal problems with this situation.
First, a dynamic entry is a complex and dangerous ballet. Friendlies with guns, innocent hostages, and armed bad guys are all packed into a small space. Training to perform this evolution with any degree of safety for all concerned is a full-time job. A high-level tactical team is going to spend all its time practicing so that when it has to go into action, all of this complicated footwork will be executed with the precision of familiar routine. Smaller departments, however, simply don't have the manpower to dedicate officers to this job on a full-time basis, and so their SWAT teams are much more ad hoc affairs, with levels of skill and training varying all over the map.
Secondly, there just aren't that many "Barricaded Armed Suspect With Hostages" callouts in most jurisdictions, and when you have a hammer in your toolbox, you have to start looking for nails to pound.
The net result is that, using various rationalizations from "officer safety" to "preventing the destruction of evidence", tactics and techniques originally developed to allow professionals to resolve a hostage crisis are being used by part-timers, sometimes for reasons as trivial as recovering a bag of dope, often with predictable results.
We need to take a long hard look at why we bought this hammer in the first place.