While when we started talking about the invisible walls, like the wall to block or affect the free flow, e.g. the policy for restricting entering into US, especially the one or two years after 911, no matter whether you are students, or capitalists, or professors, or terrorists, you guys will end up with the same result: being rejected by US. embassy . It's reasonable because of lots of immigration problems, but it ended up with blocking the "useful" people, idea, capital, merchandise, etc into US at the same time.
In addition to the sacrifice above, which is relatively less intense, the wall, which blocks the natural flow, also gets itself being pressed and pushed continuously, with the flow's getting stronger and stronger. Then there are holes , there are people jumping across it, there are people destroying the wall, there are strong forces pushing the wall. For instance, there are illegal immigrates, there are tragedies due to the tense between US government and some other countries. The wall may collapse in the end.
Same thing about China's firewall. Before Google's Chinese R&D branch came into China, Google was always blocked by Chinese government's firewall, let along other "harmful" websites, e.g. Berkeley's homepage, which central government found intimidated.
The sacrifice was huge day by day, year by year,
since researchers may lose chance to catch up with the most advances technology, students may lose chance to study, fresh and different ideas may not reach Chinese net citizens, and government may not be supervised and challenged effectively by people. The system will become weaker and weaker.
However, same thing, wherever there's a block, there's anti-block, same to physical walls which block flood, wind, various forms of natural forces etc. Those net citizens researched and came up with many solutions to cross the firewalls or dig holes. Moreover, activists also act to challenge those "wall" policies and decisions by governments.
Different from thousands of years ago, when our ancestors needed to use cold weapons, e.g. swords, knife, anchor, shield to attack a town and cross the wall, now there are more and more tools to empower people to fight against or walk around the walls, like internet, phone, network objects, telepresence, :) , airplane, boat…
So when to build the wall, where, how tall, and for how long to keep the wall, when to push the wall down… walls could be used tactically at the right time in the right place, but if strategically, that would be dangerous.