User blog comment:Mrlmm0605/Let's Talk Bleach! - Part 2: Hollows and Arrancar/@comment-24153155-20150608003246

As early as in the Agent of the Shinigami arc, you will find hints as to why the Shinigami don't consider Hollows evil. In chapter 46, Rukia explains to Ichigo that Shinigami are responsible to keep the balance of souls both on earth and the Soul Society to prevent the universe from collapsing. The reason why Shinigami have to cleanse Hollows is to maintain that very balance: there needs to be equal numbers of souls in both realms at all times. Hollows violate this "law" by munching on souls in order to still their hunger. As to date, it is unclear who or what decided that the Shinigami were the designated balancers. If at all, it could be said that it's the modern Quincy that think Hollows are evil and should be eradicated at all cost. But then again, those Quincy also consider Shinigami evil.

Although Yhwach's true motives are still unclear, you could actually argue that the Shinigami are evil to some (larger) degree. The question is though whether it really is about good and bad.

The Agent of the Shinigami- and the Soul Society arcs are key to understanding Bleach. I think the reason why Yhwach can't (fore)see Ishida's abilities might be just because Ishida is actually the last and youngest oldskool Quincy(Chapter 46 as well). In addition, these arcs also hint on why Ichigo and Rukia are (some of) the rightful protagonists of the series. I will leave it here, because it should be food for thought for one of your future blog posts, and I will be looking forward to reading that post ;)