So what do you exactly mean by not working?
Edit: another one is pretty close as well: http://insight.globalwebindex.net/chart-of-the-day-90-millio...
And that's just people who explicitly use it. With that kind of market penetration basically everyone knows what to do, or who to ask if they want to access some geoblocked service in the future.
Edit: Just to substantiate, many people I spoke to vaguely know what they would see if they get unfiltered internet, so there's not really much motivation to bypass GFW.
Police forces are unable to prevent people from committing crimes.
True - But police forces are phenomenally capable at both stopping a lot of people from committing crimes, and dissuading people from even thinking about committing crimes.
They also raise the barrier of entry (so to speak) for being criminal.
----
In today's day and age, a great firewall will work. The average person does NOT have the patience or inclination to go figure out a VPN. Heck I couldn't be arsed, and I am dramatically more capable than the average person.
But there's an additional risk you should consider.
Great firewalls are content to let the minority get away with accessing other sites, as long as they don't make themselves a nuisance.
Instead, they train the Average person, and the average populace to behave in a particular manner.
And that shift means that future generations of tinkerers, thinkers are the ones which will start out far removed from a natural set of ideas.