Non-native species have inherent risks owing to potential evolutionary mismatches. They're far more likely than natives to cause extinctions. Even apparently benign populations can become invasive when triggered by stressors. More nonnative spp = greater risk of these outcomes.
Nuance is important in how we treat non-native species
Claiming we should simply accept them ignores that some are very environmentally damaging
But, equally, assuming all are intrinsically harmful is simplistic