There could have been one black Celt, no? People did get around.
Why not red? I mean, how do you know there wasn't one?
I'm not sure what you mean by "red". But as I've said, people did move around. And really, "all Celts were white" is arguably far less likely than "some Celts were not white".
Except no one is saying that. They are questioning the portrayal of a "typical" celt family.
OK, so the cartoon features two people. One light, and one dark. But are the authors claiming 50% dark? And how would they represent 1% dark?
The point of depicting a "typical" scenario is that you don't represent the 1% dark. In the same way that a representation of a "typical" household doesn't include a homeless man, a billionaire, and someone in between. The billionaire and the homeless man are not included because they are not representative of what is typical.
Sure, I get that. But it's been the rule to never show blacks in contexts where we know they existed, and were even common. So a little balance doesn't seem unreasonable.
Lying is still lying, even if you feel that the lie accomplishes some political agenda that you happen to believe in. In this case, if you say that this is a typical family when it is not, then the fact that you lied for what you think is a nobler purpose doesn't make this OK.