"We needn't be teached what democracy is by HK protestors so long as such high level of censorship as the Great Firewall is cracked down." I understand you quite easily, but it is not natural. I would rewrite it as: "We wouldn't have to be taught what democracy is by HK protestors if the high level of censorship was removed"

It should be "we needn't be taught..." Teached is incorrect For more natural language, "we don't need to be taught..." would be even better.