Oh yeah, we introduced the alien European earthworms to the rest of the world. By accident and because of ignorance, so a forgiveable thing to do really, given that we are part of the planet's ecosystem, part of nature, though we seem to keep forgetting this fact. It's not our fault we're here. We can hardly be blamed that we've been so successful as a species. I wonder if the dinosaurs had constantly guilty consciences, or whether they just got on with life until they were obliterated by Mother Nature.
I wonder if we'd mind so much if, by chance, another animal than us carried an 'alien' animal or seed to another continent? I'm sure it has happened. And then what happens? Nature adapts.
Yes, I know I'm sending out a confused message. That's because I'm confused by the constantly ringing alarm bells.