Having returned from a stint in the states recently I would argue that yes we do need some sort of MPA and no it does not need to be Military, it all depends what you want it to do.
Take the US Coastguard.
Direct from their homepage.
The U.S. Coast Guard is one of the five armed forces of the United States and the only military organization within the Department of Homeland Security. The Coast Guard protects the maritime economy and the environment, defends our maritime borders, and saves those in peril.
Now although they are considered part of the military our MPA don't have to be, you could have the Navy looking after the Bomber fleet and the rest could lie with the Coastguard.
Why does SAR have to be military when the overwhelming majority of jobs are for civilians?
Surface surveilance again could be a Coastguard job with at times if need be specialist law enforcement officers on board.
It does not even need to be Coastguard it could be put out to tender to a private company,the advantage of having a privately run FW MPA/SAR asset is the reduction in costs to the Government, as long as it was regulated and maybe subsidised I don't see why it could not work.
Obviously it would not be the same as it was but it could be a cheap compromise.