"If your customers are doing things that aren't legal and are using your platform then sorry pal but you are responsible."
Be careful what you wish for. Unless you want postal services to be liable for letter bombs too. Especially considering how UK.gov, like most governments, tend to kneejerk and overreact so as to be seen to be "doing something". Gun laws, knife laws, Photographers being hassled, not to mention anti-terror snooping legislation being used to check peoples bins or where school pupils live.