In my opinion the idea that we should only plant native plants and must eradicate invasives is comparable to ideas like allowing only white people and deporting brown people.
Plants, like people, have been migrating since ever, through different means of transport like long shoots extending the area of growth and seed dispersal by wind, water or animals. There is no point in history we could point to and say “This is the distribution of plant species over the planet that’s desirable and we should strive to return to that.” Just like there’s no point in history where human people were distributed on the planet in a perfect way we should strive to go back to.
Hmm, immigrants are called like that because of made-up lines on a map and a history of colonialism, so I’m not sure something is true because we call it so. And it’s not always like you describe. Lots of non-native plants blend in well and start taking functions in the ecosystem. In many regions native plants cover large areas in the same monocultural way you describe for invasives, for example the white broom that covers all the mountainside here. Nothing else grows there, people hate it, but it’s native. What it does: it repairs the soil, in the long term. And I suspect that while so-called invasives might be damaging in the short and medium-term run, they will improve the ecosystem in the long run more than human intervention, because that’s what plants do. Bare soil is a bad problem, so I believe that removing the plants without immediately filling the empty space with some other plant is more horrible than just leaving things alone.
Edit: changed ‘Nothing else grows there, people hate it, but it’s invasive.’ to ‘Nothing else grows there, people hate it, but it’s native.’