This is not how I'd frame the issue. If race is really unimportant, in the sense that people of all races should be treated equally and have the same rights, why is interracial marriage "good"? Ideally, it shouldn't be an issue, so it wouldn't be good or bad. Saying that is good somehow suggests that it should be promoted, which sounds like a discriminatory statement.
This is not how I'd frame the issue. If race is really unimportant, in the sense that people of all races should be treated equally and have the same rights, why is interracial marriage "good"? Ideally, it shouldn't be an issue, so it wouldn't be good or bad. Saying that is good somehow suggests that it should be promoted, which sounds like a discriminatory statement.