That's the thing, from what I read these pamplets were advocating the death penalty for gays. That's a legal function of the courts, so what they are proposing is a change of the laws to suit their views. That's little more than a political opinion.
Now if the pamplets read: "Go out and kill yourself a lovely human!" then by all means arrest them, but unless they are directly advocating or commiting criminal acts then I fail to see the problem.
Here in the USA I could literally submit a bill to my congressman that all non-white males should be imprisoned or killed by law, and I could rally support on that basis. In the UK I'd be put in jail.