The law is quite clear: if your behaviour leads to or is likely to cause a breach of the peace - then you are at fault and could be prosecuted.

You shall not lie with a male as a female, it's an abomination" - was one of the verses quoted by these men and I'm guessing that one or two people in the crowd that gathered around them as they preached took exception. They were not arrested because of their views...they were not arrested because they expressed their views....they were arrested because of how/where they choose to express their views. ...and yes, one can be arrested if their behaviour provokes violent or disorderly behaviour in others,

But of course..these fellows had some history of doing exactly the same thing before they arrived on the streets of Bristol and they had experienced much of the same reaction in other cities - they knew what to expect. To have the right to express a view is not the same as to be right in doing it; In this instance the law agreed with this sentiment.