They might be referring to Substack having a very open policy of having writers of any political (and other) affiliation on the platform, but I don't necessarily see it as a drawback to be so neutral.

Might be the allegations such as those made by David Farrier this August[1]

> Then, last month, Substack sent out a push notification to some users of the Substack app encouraging them to subscribe to a Nazi newsletter. Like, full-Nazi stuff. Not subtle:

followed by a screenshot of a Substack profile full of swastikas describing itself as news for the "National Socialist and White Nationalist Community"

[1] https://www.webworm.co/webwormisleavingsubstack/