But for Thomas, it's not just conscience that leads him to tackle such potentially bleak issues - he also believes there is an innate humour surrounding them. Not perhaps in the topics themselves, but among those taking action to confront it, more often than not including the comic himself.
"I think it's naturally funny that the chief executive of a multinational like Balfour Beatty would ever want a meeting with a comic," he says. "So are the excuses people use to justify the unjustifiable."
But much of the humour he finds comes from the activists themselves, rather than the awkward squirmings of those trying to defend themselves.
He tells as story of black churchgoers and gang members holding a retaliatory march past the homes of Ku Klux Klansmen in Ohio - causing the white extremists to flee the state. "That's innately funny," he says.
"And just look at some of the banners they have on marches: 'If we wanted Bush as president, we'd have elected him', that's brilliant.
"Direct action is theatre - fun, but theatre. For example, we tried to inspect weapons on nuclear submarines at the Faslane Naval Base by launching a pedalo, with me and a lawyer peddling like fuck across the water.
"And some friends who tried to get into Aldermaston laid out some toy guns for them to investigate as a gesture. Silly pranks like that, or a Crusty screeching up in a battered white van with UN written on the side."
Thomas's adventures at the Rosyth naval base came for a Channel 4 show investigating Britain's weapons cache, the first one-off he has made since his series ended last year.
"Some of it works very well, and other bits suffered because Channel 4 originally asked for 40 minutes, them made it 24 - so we've had to cram stuff down," he said.
And, with the impending war against Iraq, it's no wonder that such topics also form much of his touring show, A Minor Celebrity Discusses War Crimes - a title he jokes was explicitly designed to keep people away.
"I think most people know what I do by now," he says - an assertion which naturally leads to the argument that he is only preaching to the converted.
"There's a slight myth about that," he says. Although it does reaffirm that we've all got the same basic values.
"For example, in the early days of the Terence Higgins Trust it was amazing at the end of benefits when there would be a silence, and people would shout out the names of lovers who had died from Aids.
This was at the height of anti-gay hysteria. It was very moving - and people would know that they weren't on their own." And even those who already share Thomas's views could always do with a bit more ammunition.
"There's a lot of information that people don't know," he said. "For example, that since September 11 there have been 90 bombing raids on Iraq, or that the UN weapons inspectors were not expelled in 1998 but were asked to leave by the Americans who used it as an excuse for four days of bombing."
He concedes that many will see his shows to assuage their liberal guilt without the need to actually confront the atrocities he highlights, but that others go away inspired to take at least some action.
"It's about feeling that opposition is not just morally right, it's actually a fertile ground for people to play around in," he said. Thomas, of course, has seen the results of direct action. The most successful being the successful three-year fight to halt the Ilisu dam in Turkey, saving an estimated 78,000 Kurds from being displaced. "We defeated seven mulitnationals, a Swiss bank, seven export guarantee agencies and an evil, torturing state," he rightly boasts
"But we often don't see the full impact of what we do. One simple example: in the Vietnam war, Nixon had the nuclear option, but Henry Kissinger warned him 'Never underestimate the hammer blow of the peace movement'. It shows protest gets through.
"Homophobia was quite intense in the early days of HIV, but we got through it. Asylum-seekers - we'll get through that, too."
Yet despite the range of his campaigns he gets involved in, Thomas insists he's no full-time crusader. "Most the time I'm worrying about the bills or taking the children to swimming lessons," he says, "just once in a while, I'm doing the things I ought to be doing."
"I'd feel an utter shit if I didn't. Morally, I wouldn't feel comfortable to walk away."
Mark Thomas is on tour until May 28. Mark Thomas Weapons Inspector will be shown on Channel 4 at 7.30pm on Friday January 31.
Article first published January 29, 2003
Published: 12 Jul 2006