Hitler was a Vegetarian
Some people seem amazed that arguments this bad get put on billboards by "respectible" thinktanks:

Can they be serious? Can they possibly think that this will persuade anyone to doubt the overwhelming evidence about climate change, because a few people who are not only criminals, but mentally ill, believe it’s real? Can you imagine anyone with a shred of self-respect for his or her intelligence, even arch conservative climate change deniers, buying the case that climate change can’t be real because Charles Manson and the Unabomber think it is!?
I find this somewhat delightful, in that it is such a blatant and probably successful attempt to appeal to the subrational lizard-brain emotional mental circuitry, with no danger that it can be confused with anything remotely sensible. So yes, they are serious, they are unapologetically trying to bypass reason. It is not meant to "persuade" anybody of anything, simply to strengthen some Pavlovian associuation pathways in the brains of susceptible dimwits driving by. And of course it is also a successful attempt to get publicitiy, of which there is no such thing as bad.