> So having more cops in a high-crime neighborhood is somehow a bad thing, because the presence of more police actually confirms the fact that there is more of a need of police in this neighborhood?

That's the essence of the Security vs Liberty argument. Yes, on one hand it is a good thing to have more security in an area which needs it; but will you accept say, being filmed 24/7 for more security, with the tradeoff that this same data can be analysed by third parties for any reason whatsoever (ala Minority Report's shopping mall scene).

It is not an easy problem and we must decide for ourselves which tradeoffs we will accept, because it is seldom free technology with no strings attached.