OK, I'll explain. We have no obligation to give recognition to random celebrities just because they happen to have something that interests us. Specifically with this case, the author of Blacksad apparently... at the end of the comic, there is a phrase that indicates detest towards animals. I bet he'd freak out in a furry gathering!
Indeed, we don't have an obligation. (We don't even have an obligation to have a GoH at all.)
However, being a GoH is not an award, nor a present to the person in question, for whatever reason. GoHs are invited because the responsible con staff believes that they:
1. Have done something that is relevant to furry interests,
so the patrons are interested in their work2. Are able to do some kind of presentation regarding that "something",
so the patrons can have more insight in the GoH's line of work3. Are neither freaked out by furs, nor be gruff and unsocialized, but rather interested in people and the community,
so patrons can actually approach them and talk to them.
(The latter point is, of course, difficult to judge, but we can safely assume that not responding to invitational mails is an indication to the contrary.)
GoHs are invited
for the patrons of the con. They are part of the program. Being GoH is both an honor and a responsibility.
Now, if you select a GoH for a con, how do you approach the task? Naturally you try to get people from outside the fandom, because
1. They are normally not so easily approached, so you might put the weight of a major convention behind your request to get them interested at all,
2. They are not normally found at furry cons, as opposed to many interesting and well-known furries who might make a good GoH but whom you can meet at every third convention anyway!
By these standards, the "Blacksad" guys are by no means "random celebrities", but pretty relevant. Naturally that doesn't mean the con should invite anybody just because he/she puts animal heads on his/her works...
At the same time, it doesn't exclude people from the fandom itself. For example, on an European con you may want to invite American artists who normally do only the US cons, and vice versa. You might want to invite people who normally don't go to conventions at all. You might want to invite people who do go to conventions, but they are not spotlighted, or they don't do panels about their work on their own. You might even invite a GoH just because you think he/she is not widely known but deserves to be popular because of his/her quality of work.
Choosing a GoH is a multi-faceted process. And not everyone who is deemed suitable will be available in the end, anyway.
(As for the remark on "beasts" in the (first) Blacksad comic, I wouldn't lie too much weight on it; clearly the furry representations of the characters are not chosen because they are so fuzzy and cute, but to represent personality types, and naturally a countering comparison lends itself to the context.)
