The concern as I understand it is not that a journalist would just straight-up defend a conspiracy theory. Rather, the concern is that if you give any airtime to conspiracy theorists, even in the form of a debate, some viewers/readers will conclude that there must be some nugget of legitimacy in the conspiracy (why else would it be on the news?). Indeed, conspiracy theorists have relied on this to gain support, especially before they had the internet, when strategically baiting the media was the only way to get their bullshit noticed.
A far greater concern than conspiracy theorists getting taken seriously are actual conspiracies perpetrated by mainstream media outlets. I gave two examples elsewhere in the thread: Weinstein and Epstein. Those aren't "conspiracy theories", they're know and active conspiracies. There were a multitude of opportunity to report on them but the stories were actively stifled for personal and political gain.
That was deliberately a less controversial one than climate change, and newspapers publish denialist claims of basically the same level of substance as flat Earth ones all the time (e.g. James Delingpole)