Debating lunatics is a choice to handle with great care

A perfectly respectable position.

Nick Griffin's appearance on Question Time has sometimes been held as at least partially responsible for the subsequent collapse of the BNP. Brits are not fans of Trumpian politics - no, not even the Tories who are trying to appease the racist Oompa Loompa across the pond, not really. A well-moderated discussion would likely hurt Bannon a lot more than any benefits of exposure : his ideas gibberish are simply too far outside existing norms to gain respectability with a program or two.

That said, the BBC has consistently failed to adequately examine the self-serving hypocritical nonsense that Farage is wont to vent from his anus mouth, so Sturgeon's choice is probably a good one. Getting politicians to debate with such a lunatic doesn't serve anyone : rather than elevating Bannon, it just denigrates the others even further. You can't have a sensible debate with a lunatic. It's better to avoid such things entirely.

https://www.theguardian.com/politics/2018/oct/20/nicola-sturgeon-quits-bbc-event-over-steve-bannon-invitation