It tells me you're still trying to find something to demonize without understanding the base culture, which doesn't regard religion in the same way as the West tends to, which is based in affiliation and an us versus them mentality. Japan is more eclectic and syncretic by comparison, saying that these religions should be able to coexist, even if they disagree on things, because they all seek meaning in life, which is a very human pursuit that is common ground.
Of course, Solomon didn't control demons in the Bible, it's considered non canonical, if I'm not mistaken. And Rin is the son of Satan, but he's not innately evil because of that: in fact, he's the protagonist.
It tells me that, contextually, there's a major difference in storytelling between someone willingly making a contract with a devil or demon, which could be considered, in general, an ethically questionable action regardless of believes in devils as real or evil, versus someone merely having a heritage that people associate with evil, but that they aren't evil in and of themselves.
Naruto has what many call a demon in him, but he's not evil, nor is the "demon" actually innately malicious. Rin, to my knowledge, is the son of Satan, but unlike some of his other half siblings, he's very much a good person, if very chaotic and disregarding of rules. Blue Exorcist seems to have that notion of nature versus nurture, with nurture leaning towards how someone can be good or evil, regardless of heritage.
Someone could have heritage from an angel in a series and not be considered a protagonist or even a positive role model in the slightest, but repressive and generally not someone you want to emulate in the slightest because they're more like a church inquisitor in the common stereotype than someone who seeks good, but also follows rules in a reasonable fashion.
. If you're interested in talking to me personally add me as a friend via some "instant messenger" or preferably Skype. (PM me your "instant messenger" or Skype name so you don't have to post it publicly 
