There's a fine line between retaining the existing culture and gentrification. Both can be had at the same time, but it must be cautioned that gentrification (full blown), tends to kill the culture and steer it predominately towards one side. Its not heterogeneous in other words.
Brooklyn can grow, but it must not lose its character. The byproduct of growth is change, no doubt, but it can't be 0 to 100, where 100 is in favor of "X" side. What makes NY great is its melting pot nature. Without it, without the chaotic nature of the soup called life, the city would suck. Fortunate it is not the case.
I think what he's referring to are the criminal elements (but its not gentrification that eliminates crime but better police work and presence). Its a far-cry from the 70's, but the city has seen a decline in crime, and with a booming area, police presence is always ticked up a notch and more eyes on the street (more folks outside). So naturally, it will become safer. No worries!!!