Before you talked about the Fediverse as a whole, now from a single user perspective.

IMO it affects the Fediverse as a whole by abusing it. The whole idea is an open network, where instances can federate with each other to bilaterally share information and create a seemingly single platform. This is not the case with the planned Threads integration, because they explicitly plan to feed on the content, but hiding sharing their own content behind an (for most of their userbase) obscure opt-in.

From a single user perspective it doesn't affect you directly. But it affects the platform you are part of with malicious intent.

I am not against Threads joining the Fediverse, and I do actually think it would be great for the growth of the Fediverse if actual big players join, and if it brings content that I personally do not like to see, I can use the tools available (e.g. blocking user/communities/instances) to hide it. But only if they plan on joining as a "regular instance" like any other - but Meta does not intent doing so, since they have chosen the opt-in with obvious intent of simply gaining additional content on their walled platform for their own gain.