If you're against paid administrative leave in this circumstance, then you are either

A) Against it in all circumstances, including those where it is obvious no wrongdoing occurred and the subject will be exonerated, or

B) Automatically assuming he's guilty, will be fired, and could have been fired immediately if it weren't for those pesky rules saying we need to prove he did it.

Given you're apparently unaware this process is the standard for any unionized workplace, it seems likely that you just have some ideological beef with the police, and see police unions as an extension of the police rather than a union protecting its workers. If you're against collective bargaining, you're against job protections such as requiring investigation and cause for dismissal.