Sure, but let me give you the same example but in a different context.

Let’s suppose that instead of “let’s lock up everyone from this ethnic group”, a politician says “let’s stop illegal immigration”. Stopping illegal immigration is a perfectly rational, reasonable, moral stance to have. If someone hears the latter phrasing, they might take it at face value even if the politician really means the former. Thus, this individual has come to indirectly support the former even though they think they’re supporting the latter. The end result is the same because the politician’s intentions never changed, however, the morality of this individual is no longer as black and white as in your example.