The Insurrection Act requires a State governor or legislature to request military assistance during an insurrection. The act also allows the president to act without that, if the State is not acting in a way that is protecting people's rights. This is why Bush could not deploy the National Guard during Katrina - the governor of the state refused to request the help, and it was not deemed to have come to a point where the president would impose the military anyway. The last time this act was used was during the Rodney King riots, where the governor of CA requested assistance.
This is a long way to say that we have made it difficult to deploy the military or use military force within the US. And for good reason.
So, why do we allow police departments to arm up and look/act like the military? If it looks like a duck and quacks like a duck - is it not a duck?
I get that there are circumstances where SWAT may be required, but why does every PD have a SWAT team? Why isn't it required that the governor authorize the use of SWAT in every case?
SWAT is now routinely used to perform dawn raids (no knock raids) on people who have no criminal record, and where no violence has been reported.
Controlling the equipment may be part of the solution, but it won't do any good unless the deployment of SWAT and other military style options are more carefully, judiciously, and transparently controlled.
You consider the Posse Comitatus act as being passed for a good reason? Perhaps the effects are good, but the Act itself was mainly passed so that the white former slaveholding states of the south could enforce racially charged laws without the Union military preventing them.
Just because you don't like the particular use case doesn't detract from the fact it is generally not desirable to be throwing around your military at your own people at the drop of a hat.