It is akin to embargo ethics essentially. Technically buying coal from North Korea can help feed the people but by supporting their government you help prolong their power and thus lead to more suffering. It is ethically messy on the right side even.

Similarly by not giving them access to what they know the rest of the world has you breed discontent with the current way of doing things. The culture and thus indirect demand flows regardless of what they do like rock music into the USSR. It also isn't an absolute denial - google would gladly step back into China with no ethical qualms if they abandoned their censorship policies. Their government would find it unthinkable however.