Something I wasn't aware of before this event is that broadcast licensees, such as ABC, are required to 'serve the public interest' as a component of receiving and retaining their broadcast license, probably because there's a limited number of such licenses available and they are publicly broadcast for free. It's a significant aspect of their operational obligations including each renewal requiring a further description of how they have continued (and will continue) to serve the public interest.
This is not the case for cable licensees, which goes a long way towards explaining why ABC/NBC/CBS/etc have all remained relatively sane in an era where it's clearly become most profitable to pick a side, pander, and confirm their every possible bias. This is because e.g. Fox News or MSNBC can get away with far more than ABC. And this is probably simply an example of something that you cannot get away with on public broadcasts.
Deciding to try to 'joke' about a domestic political assassination, for which countless people are still grieving was dumb. Stating, "We hit some new lows with the MAGA gang desperately trying to characterize this kid who murdered Charlie Kirk as anything other than one of them." was very dumb. I think the only issue that makes this debatable for people is the radicalized nature of politics.
If this had been a white wing extremist who murdered a liberal guy who made a living posting public (and atypically respectful) debates, and Kimmel was then mocking it in a similar way, while further implying that killer himself was a Progressive or whatever, then obviously nobody, and I include conservatives there, would see any issues with him being canned.
The decision to preempt ‘Jimmy Kimmel Live!’ was made unilaterally by the senior executive team at Nexstar, and they had no communication with the FCC or any government agency prior to making that decision,” a Nexstar spokesman said.
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Immediately following his monologues there advertisers and affiliates contacted and were complaining to Disney. The FCC was, if anything, just the final nail in the coffin.