There have been incidents like the Oaksterdam raid where the DEA took up all SWAT resources for a raid of a civillian, unarmed (and legal state-wise) marijuana cooperative. Meanwhile, there was a school shooting minutes away. [1]
The reality is that crime is falling in the United States and has been for a while (Freakanomics has a decent piece about the relationship of crime and the availability of abortion, with a time lag in the former that showed a correlation with the latter) and I think this paramilitarization is an attempt to fill up budgets and give reasons so that they aren't reduced in the future.
[1] http://www.washingtonpost.com/blogs/blogpost/post/oakland-sc...