Time to throw down some notes.
1. While Peter has acquired national treasure status, as an activist and courageous human being he has shown time and again a willingness to put himself and his safety on the line for the liberation of LGBT people. So when a little known NUS rep makes claims that go beyond fair criticism and are borderline libellous, you can understand why a fair few people are incredulous.
2. Germaine Greer remains the country's best known feminist thinker, and she has several controversial opinions that arguably contradict the thrust of her politics. Scrapping the right to anonymity for rape survivors is one, and being a card carrying LibDem throughout the period of the Coalition government is another. Her views about trans people are well known and are out of step with the growing momentum behind trans acceptance. By showing solidarity with her when she was targeted for disinvitation (she wasn't no-platformed) by a campaign led by Cardiff union's women's officer, Peter could have been perceived as being 'soft' on transphobic matters.
3. No platforming operates according to a certain logic. It is necessarily censorious, but is not simply so. As longtime readers know, no platforming is a tactic that emerged in the anti-fascist struggles of the 1930s, though the term only came into common currency during the 70s. To 'no platform' meant taking direct action, often violent, to prevent fascist organisations from running marches, holding meetings and rallies, and to deny them any public platform at all. This wasn't because they were nasty, it's because it was part of a life and death struggle for political space. Where that fight was won by the brown shirts and black shirts, the hell of Fascist Italy and Nazi Germany tells you what exactly was at stake. To reiterate, no platforming was something that was enforced by the martial power of communist, radical, and labour movement forces. It was an expression of working class confidence and power and not the state or some other institution denying fascists meeting rooms.
4. What has been happening in our universities, be it Germaine Greer, Peter Tatchell, or Maryam Namazie somewhat falls short of no platforming classically conceived. But times change. Come the 1990s and 2000s, the tactic had been transformed into a principle, mainly by the SWP who were the chief "inspiration" behind the Anti-Nazi League and then Unite Against Fascism. Unlike Red Action and Anti-Fascist Action, who still physically confronted and violently assaulted fascists well into the 90s, direct confrontation was the exception rather than the rule for the SWP. Activities were centered around making fascists into political untouchables - debate with them was to be avoided as that granted them legitimacy. Likewise mainstream politicians, especially of the labour movement, were called on to refuse to share platforms with them, be it at hustings events or election counts. It also meant protesting outside venues where fascists, such as the BNP, had been given a platform by a third party. That "classic" Question Time episode with Nick Griffin being a case in point.
5. There are a whole lot of other things going on with the attempts to no platform established activists, not least generational dynamics. But sticking with the logic of no platforming, it does make a contribution. As activism and politics is a key marker of personal commitment and identity - at least among those who care about such things - a logic of by their friends shall ye know them comes into play. It's not a matter of so-called virtue signalling, which is an invention of the right to explain away why people opposed to them sometimes hold radical views, but rather a concern that debating, in this case, someone with imputed transphobic views somehow grants those prejudices a legitimacy they shouldn't have. Hence the best way to stick up for trans people and other minorities is to not give naysaying voices any credence - especially when they tend to have the mass media at their disposal, anyway.