You would think that some things are just so racist that, on encountering them, everyone—even white folks, almost to a one—would say "holy FUCK that is some racist-ass shit, what the FUCK are you even thinking?" A sort of Maximum Ignorable Racism Threshold, if you will.
Apparently you'd be wrong, because you can be the most vilified racist shitbag in recent memory and still have people going to bat for you in the mainstream media: arguing that happened to you was wrong, telling people they should "calm down" over your racist remarks.
If this supposed threshold did exist, these racist-ass shirts would never have seen the light of day. Like, seriously, just think how many people have to have been party to that production, with none of them raising sufficient hue and cry to put a stop to it.
I sorely doubt that this is much of a revelation to anyone who's not carrying around a gigantor sack of white privilege. Chalk that up to yet another example of how privilege works to hide the realities of the rest of the world from people possessed of it.