The two aren't mutually exclusive. Journalists have an ethical responsibility to be honest, but outside of that there's nothing to say that a journalist cannot have a set of beliefs that shape their worldview.
In this case you aren't really accusing the NYT of being dishonest, you're saying that their honest opinion isn't ok because you have a different opinion (or that a journalist has to be void of any opinions at all). I'd just suggest you skip either that author's work or the NYT in general then, and find something more aligned to your own worldview.
As to the accusation it is "activism?" I mean, yeah, I guess. Arguing that something, anything, is wrong is activism depending on your definitions but since we haven't established that activism is a bad thing or wrong, that's not really problematic in and of itself.