One of the speakers at a recent conference on disagreement argued that 'No platforming' is really a matter of distributing scarce goods (platforms in respected venues, basically) rather than one of free speech.
In one sense, I would agree, but I suggest that it is in the nature of 'free speech' as a political, or indeed social, right that it depends upon being permitted to put opinions, arguments, programmes, etc., across on platforms that can draw attention and make an impact. This can include actual governmental institutions like parliaments, council chambers and so on. In these contexts at least, the proposal by the conference speaker to apply a principle of 'positive invitation' rather than just excluding undesirables, will in effect apply, for instance through either need to win seats or secure a minimum level of support to gain representation.
Indeed, the current German political crisis over how to avoid the AfD being involved in government (never mind being able to put their point of view) shows how exclusion can only work if the people excluded have only a relatively insignificant level of support. Democracy naturally tends toward positive invitation rather than exclusion.