he camera itself might be a tiny, tiny fraction of the salary of a cop, but it would still require a massive database and supporting infrastructure to run/maintain the entire implementation. Nor would it change the fact that people would still bring (founded and unfounded) lawsuits against the police.
Don't be ridiculous
We already bear massive costs of litigation and document storage.
This saves money two ways, Cops know they are being watched, and criminals can't make bogus claims.
The cost for several years of operation would be offset by the absence of ONE riot or bogus lawsuit.
The whole thing can be automated.
You come in from your shift, put your cam in bin, it gets copied to bulk storage.
Key in your badge number, (maybe RFID) and machine dispenses an empty camera every morning.
(Hint: storage is dirt cheap the backup/storage/indexing etc deletion can be entirely automated. )
If all you did was patrol and never had a single arrest or confrontation it gets purged in 90 days.
Every day, there better be video on the camera, or Internal Affairs is going to want to know why.
By the way: for every ridiculous example you cite there are 33,000 arrests every day that are not convoluted contrived cases. And even in the situation you describe the police video would not be enough to convict anyone. Saying you should not have evidence because you can contrive a situation where it might not be the whole store is tantamount to shutting down all scientific research world wide. You, sir, are an idiot.