Actually, they kinda are:
and
I guess it makes enough sense as far as it goes.
Just in the interest of common decency a business shouldn't be able to claim a cartoon silhouette of an enormous penis, or an exaggerated, stereotypical likeness of an individual (something as in the image below) as a trademark.
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I guess the only real question is, "How far do you actually take it?"
Virtually anything can be considered offensive by somebody, so what's the standard where society has to step in and say, "You know what? We appreciate that you find the Nike "Swoosh" offensive because you lost your eye to a horrible fishing hook accident when you were a boy, but the "Swoosh" image is fairly innocuous and acceptable to society in general so we're going to have to go ahead and let Nike do their thing".
When you get to something like the Redskins patent and trademark you've potentially got a large number of people who might be directly offended and you're probably treading much closer to the kind of terrain where a large segment of the population would be supportive of that large number of people who would be effected directly.
Bottom line here is that I think the Redskins franchise definitely has grounds to fight this decision but at the same time I think the U.S. Patent Office is on pretty firm regulatory footing in the decisions they've reached.
While many of us may not agree with the decision, it certainly wasn't capricious nor is it completely impossible to understand where it came from or why it was reached.