Instance owners can have full control over who they federate with. From the start, the mainstream in the Fediverse has had a tolerant, open-minded and positive mindset. Over time instances that don’t follow this (e.g. by promoting hate speech) are defederated, leaving mostly decent discourse. Users that try to join instances that follows the Fediverse ethics while not belonging, and try to spread hate, get banned.
We’re still in early days but this will keep happening until the verse is wide and large, and you can choose your own little corner that aligns with what you want, whether that’s more like what we have today, or the opposite end of the spectrum, but for now we get to enjoy to still have mostly only tolerant instances, and the nasty ones are defederated into oblivion.