If they're literally incompetent or toxic (i.e. "bad"), it's obviously better to find that out during the interview process and not hire them in the first place

If they're literally incompetent or toxic (i.e. "bad"), it's obviously better to find that out during the interview process and not hire them in the first place. The 10 "potential candidates" don't include anyone that the interview process detected as bad. Interviews are imperfect, and damaging candidates will slip through the cracks. Are you seriously suggesting that a business should decide not to fire someone based on their immigration status, rather than their performance and integration with the team?