Of course I'd prevent it, and of course it means everything. I'm just saying that it's incredibly easy for terrorists to identify, without the help of Google at all, specific areas where humans congregate in greater numbers in order to increase the casualty count when their aim to to do so. Hence many terrorist atrocities that have already occurred have done so in places like airports, train stations, music/sports venues etc.

Moreover, these are venues with serious capacity and are unlikely to be the kind of places where users of Google's new service will look for. They're more likely to want to know, "Is my favourite downtown bar busy?" which might represent a few hundred people at most, whereas the average sports stadium is always busy when a game is on, and holds significantly larger numbers of people.