[BPSDB] It seems a good idea to run a proxy like Squid or (perhaps better) an anonymizer like Tor (because Squid is not anonymous) to give internet access to users in other countries where the internet is not free. It’s something you can easily do with a small investment of time and some of your spare bandwidth. But you should be aware that not only Iranian or Chinese dissidents may use your server. Your local plods may note that something nasty is coming from your IP address, as happened to this man who found he was inadvertently distributing child porn or this one who found he was liable for a bomb threat.
The law currently appears very uncertain in the UK over the liabilities of server administrators for what passes through their systems. So far it seems that no-one has been convicted of anything in the UK arising from the use of an anonymizing server, but be aware the police are unlikely to have much expertise in this area, and you may lose your equipment for some time while they try to pin a terrorist or child porn charge on you. In the current authoritarian atmosphere it is most likely that any legal doubts will eventually be settled against the admins.
In accordance with my theory that all authoritarians have more in common than their superficial political differences, note that if you are arrested (even if not convicted) while trying to assist dissidents in authoritarian countries you will lose your eligibility to visa waiver if you visit the USA.