Like askG said, it IS fashionable right now to be "street smart".
But schools are not the streets and we shouldn't look at schools as if they are - meaning we shouldn't impose street mentality (which at the lowest common denominator represents unlawful, immoral activity) on our students. You say we're grooming our kids to be "informants", but by not doing this, what are we grooming them to be? Standers by while ignorant sons of bitches run around negatively impacting others lives? Well, "As long as it's not happening to me", right?
Honestly, I'll be the first to say, "mind your own business as long as you're not directly being affected by the stupid behavior of others", but sometimes you end up in a situation that indirectly threatens your well being and or lively hood and you have to take some kind of action.
The people who look at "snitching" as basically a crime are the people who are worried about getting snitched on. Basically these people are doing things they know damn well they shouldn't be doing (the unlawful, immoral behavior I spoke on earlier). If you don't want to get "snitched" on, don't put yourself in a situation where someone may have to drop a dime on your ass.
