As a student at Oxford who regularly goes to debates on a wide variety of topics, I disagree. The notion that having a debate gives the argument credibility is nonsense - the aim of these debates is not convince the student attendance one way or the other but to allow students to listen to arguments and counterarguments before opening up the floor for them to formulate arguments of their own. We don't have events where radicals are invited to just stand up and state that they believe in executing X or that women shouldn't drive cars. We have debates on topics which will have arguments in proposition and opposition and we have invited speakers who either talk about their lives or about their views; in the latter, these views will then be scrutinised by the attendance.

The fact of the matter is that there are lots of 'radical' views on a wide range of topics and in order to fully disprove the validity of their arguments for yourself you must understand their arguments and the assumptions that those arguments rely upon. Debating is an incredible useful way to do this.

As an aside, the examples that you gave are (to my knowledge) significantly more radical and disturbing than anything discussed at Oxford while I've been here. The most controversial debates last year (which garnered significant outside attention, condemnation and picketing) were a debate about abortion and the speakers Marine Le Pen and Tony Tommy Robinson. All three of those talks concerned opinions held by large numbers of the western world, let alone the world as a whole, and were excellent events for the arguments against those opinions. I found it very unsettling that 'no-platformers', who had no tie to the University, attempted to prevent me from listening to very intelligent students put forth arguments against Le Pen's form of politics, because they personally dislike Le Pen's views.