Furthermore, OpenJDK is licensed under the GPL. Even if Oracle stopped contributing to OpenJDK the GPL license would ensure that OpenJDK and all derivative works can still be freely distributed and are still subject to Oracle's original implicit patent grant.
I don't see how that's relevant? I wasn't aware of any aggression towards Google, until Oracle suddenly decided to aggress. The fact that Oracle hasn't been aggressive towards non-Oracle OpenJDK distributions in the past doesn't mean they won't be aggressive in the future.
I can probably agree that Oracle is relatively unlikely to start coming after people for patent infringement related to using OpenJDK or forks thereof, when OpenJDK is licensed under a license with a patent grant. My biggest concern is just that Oracle seems like a thoroughly evil and unpredictable company, and I wouldn't like to use technology they own and which uses patents they own. I wouldn't have imagined that Oracle would ever come after people for re-implementing their API; I can't imagine what Oracle will do in the future, but I won't build a business or institution around the assumption that they will do nothing. It's not like there aren't a plethora of other solutions for anything developed by Oracle, most of which are better than Oracle's alternatives.
I think that even if it made sense to assign virtue judgments to corporations, it would be a huge stretch to claim that Oracle is any more evil than other companies of similar size, like Google, Facebook, Microsoft or Apple, but as I work for Oracle, I'm obviously biased.