You are responsible for all traffic coming from your droplet. In many cases you will be warned before any action is taken. We host several VPN services but the difference is that they have registered users and can take action against abuse or illegal activities. With a public proxy you do not have the ability to deal with these issues effectively which could result in your account being locked or suspended. If you wish to contribute in this way, I would recommend running a TOR relay node (not an exit node). In this case you would be helping people to reach information and avoid blocks or monitoring by others while still protecting yourself and your account.