As Ofcom have said, there is nothing wrong with broadcasting even very controversial content - however, it always needs to be presented with context or countered with differing opinions (especially where mainstream opinion differs). GB News / Mark Steyn could have avoided this entirely by having someone with an opposing view argue with her, and/or by clearly (and repeatedly) stating that these are her personal opinions and that they differ from what the authorities / science community believe. Ofcom don't mind if you leave the audience to make up their minds about a controversial opinion, but they do require that the audience are informed that there are alternatives.
As Steyn and others have pointed out many times however, this principle has been applied in a very one-sided way. In this particular case, there were all manner of claims broadcast that rather dramatically *overstated* the safety and efficiency of the covid vaccines, and Ofcom never reprimanded or fined anyone for not 'balancing' those by someone more sceptical. The fact that one side reflected what the authorities and their hand-picked scientists wanted us to believe, and the other did not, combined with the guidance that was issued by Ofcom at the start of covid that basically said 'you can't question what the state says on these matters', makes Ofcom appear more a state censor than an arbiter of balance.
The crux of these issues though is that they basically just contracted these shows out to Mark Steyn, who has no knowledge of UK broadcasting regulations, no fear of the regulator and no desire to do what he's told to do - hence his throwing his toys out when he got told he would become liable for any fines he might accrue.
That is basically true, yes. Although I maintain, as I said at the time, GB News needed him more than he needed them, so I don't blame him for walking away.
His attempts to appeal these decisions will go nowhere, simply because there is no right to complete freedom of speech in the UK, and the rules that he broke cover everybody.
I don't think they will go anywhere either, sadly. Though I'd hope they did, not least because the government is dramatically increasing Ofcom's powers via the Online 'Safety' Bill.