I haven't seen any locals state that it is "shocking and unacceptable behavior." Please do point those out. Even if they did mention that, the only thing shocking and unacceptable is all of the クソ馬鹿ぼんくら stuff.
Actually, ironically, if he had just said, "ugh foreigners!" that would have been more racist than the things he did say, because it would indicate that he thinks the word "foreigner" itself carries all the negative implications he was trying to get across - that foreigners are inherently bad. But he didn't. He felt the need to tack on a whole bunch of epithets to modify the word "foreigner" in order to get across the negative feelings. To him, "foreigner" alone didn't convey disapproval.
Thank you.
I asked my wife and a couple of friends (the closest native Japanese people I have to hand) and they expressed a similar reaction. While "gaijin" can have negative connotations when used in the wrong context, it's all the stuff preceding it that's over-the-top or harsh in their eyes.
Obviously a few more personal accounts don't exemplify the whole Japanese mindset, but to all the people saying "omg you guys defending him", maybe we're simply trying to defend/explain a culture we're attempting to integrate into, rather than immediately dismissing it as ignorant and offensive based on some Tweets and translations.
Also, regarding the whole "chewed out by Inaba" thing, I'd like to point out that Inaba himself posted the (rather amusing) exchange between he and Kamiya on his own Twitter feed, suggesting that the whole thing was treated in a lighthearted way. You can take offense to it if you want, and not many will argue that Kamiya is the most polite guy they know, but it's not going to harm him, PG, or the industry. It might harm your perceptions, but everything else is perfectly safe.