If you think loyalists only rioted because of online discussion on mumsnet - or indeed anywhere, maybe you should have a look at what's happening around Northern Ireland this evening - and remember that these events long predate the invention of the internet.
And it wasn't really misinformation either: the police now say they still don't know whether Hadi Alodid is Somali, Sudanese or, now, possibly Chadian. So a man travelled via Paris to Dublin, then to Belfast all on (presumably) fake papers.
IMO it's perfectly reasonable to think that MORE discussion should be allowed on matters such as how migrants travel in and out of the country without justifying riots. I would suggest that the police trying to control the dialogue, instead of arresting offenders, including rioters, is part of what causes social unrest when attacks like the Belfast stabbing or the Southport killings happen.