In some good news, the University of Warwick Students' Union appears to have backed down unequivocally over its earlier decision to no-platform Maryam Namazie. They have indicated in their statement that they'll be apologising to her.
As far as I'm aware, we can take this at face value. That being so, the people who made the latest decision deserve to be commended.
There are more general questions about the circumstances in which it's okay to disinvite or veto (or no-platform) speakers. I'm leaning very heavily against doing so, though there will be extreme situations, and as I've often said I am not an absolutist about such issues. However, the Namazie case illustrates yet again how well-intentioned rules and restrictions can soon become overly broad, and even perverse, in their application by zealots.
Sometimes bad decisions can be reversed, as happened here, but not everyone has the time, energy, resources, and support for the fight.
It's best to subject restrictions such as these to careful and sceptical scrutiny when they are proposed in the first place. It's best, too, to have a bias toward very narrow application of such rules, once they're in place, restricting them as far as possible to extreme, unusual circumstances.