A reader writes (in regard to the above picture):
Technically that's an armored personal carrier not a tank. I see nothing wrong with SWAT using APCs since they are trained for things like terrorist attacks, foreign invasions, mass hostage situations and sieges. Shouldn't be used to break in people's walls for selling $100 bucks worth of crack though. The thing to remember when it comes to "militarized" police, is that in the event of a devastating crisis, the only military that can be deployed on US soil is the national guard. So if shit hits the fan, you can really only rely on the police and armed patriots to defend us.
While the vehicle depicted is obviously not a tread-driven assault tank, it is an armored vehicle designed to be deployed to fight foreign enemies. It is, however, equipped with mounted guns and, when bearing troops as it is designed to, can be utilized in aggressive military-style assaults not unlike a standard tank.
For the purposes of the point being made (and being made within the bounds of hyperbole allowed in the meme medium), we felt the distinction was not necessary. That being said, you are absolutely wrong about SWAT's proper role as a policing body.
The military will always be the military. The National Guard might be the first to respond in such an event, but the whole of the military would most definitely be the ones to respond to foreign invasion. SWAT may claim this as a means to justify their existence, but they are absolutely wrong, and it's a shield they use against criticism.
We posted this meme at Metafederalism in order to highlight this fact. Police are supposed to be a non-military force that protects it's citizens, not a military unit, and their blurring of these lines over the last few decades has been the root of most of the problems were facing with police today, whether it's overly aggressive policing as in the case of the War on Drugs, poor accountability for misconduct (remember, the military has its own entire justice system, civilian police are subject top the same laws as you and I, or at least they're supposed to be), or even smaller things like the police attitude that they are a class of their own and "civilians" (a.k.a. the people they're supposed to be serving and protecting) ought to be beholden to them.
The folly of military-style troops guarding the peace among the citizenry is exactly the scenario that the 3rd Amendment was made law to prevent. For further reading, I recommend Radley Balko's Rise of the Warrior Cop.
Now don't get me wrong, police and "armed patriots" have perfectly legitimate roles and we fully support the 2nd Amendment, but if some foreign power were to invade the U.S., I want the finest military in the world defending me, not some bullies who receive less than 60 hours of firearms training and can't tell the difference between a gun an a taser on their hip.