So my next question is, isn't what we're doing as a species more or less natural?

It is, imho, and "infestations" are indeed a normal part of ecosystems.
Only few species had global impact tho (and none in the timeframe of a geological second), we arent the first.

infection has too many negative connotations that are unfair.

I would say that we embody (literally) all of those negative connotations actually, ofc with some weirdness, like how many billions of chickens now live bcs of us.

I do struggle to find positives in our interaction an consequences to the planets ecosystems.

What gives us the audacity to justify the loss of biodiversity on such a grand scale?