I saw Mark Thomas in Swindon (U.K.) recently. Yes, he was funny (and a good story teller). But he hijacked a comedy evening to protest at the Yusyufeli dam project. When we left, people stood outside collecting money for the project.
Most people go out for a good fun evening, not to be preached at. I consider myself sane enough to make up my own mind on issues like this. I wouldn't see him again!
Mark Thomas denouncing the JWs - UN involvement, etc? I don't know. . . I think personal experiences of X-JWs is the biggest threat. People (and JWs and the org) would be a lot more more receptive to personal experiences, than someone making fun of, or campaigning against the org.
To us, JW UN involvement is a big thing because the WT has denounced the UN, etc. To most members of the public, it's probably not such a big deal. I'm sure the WT isn't the only org with corruption in it, or members of the UN, etc. Many people see the JW as a wacky religion anyway!