As a supporter of open source software, I wholly support Oracle's fight to catch Google trying to evade the GPL. I'm not sure how an open source supporter could really be supportive of your employer lifting from the paid version of a product to avoid having to comply with the GPL. Google's actions here pose a massive threat to anyone who has developed open source software funded by a commercial licensing option.
What I find dubious is not that Oracle might try to make a mobile OS (your argument against this is the subjective opinion that it was "awful"), but Google's claims that their use of the Java API was "fair use". Building a non-interoperable competitor for commercial licensing based on their work doesn't come anywhere near the terms of fair use. By Google's own admission, the choice to do this was an attempt to leech off of developer familiarity with Java rather than any sort of compatibility need.
Open Source -- as in Source Code. GPL protects source. The stuff you actually fork when you type 'git clone'. You really think Richard Stallman would be opposed to someone cleanroom re-implementing a GNU GPL'ed software from scratch that has a compatible API? Stallman called Android a major step forward, and if anything, his problems had nothing to do with subsetting Oracle's API, but issues surrounding Tivoization and binary blobs.
java.io, java.util, java.lang are re-mixes of every other OO runtime going back to smalltalk. I'm not buying this idea that reimplementing List, Map, Set, InputStream, et al, without copying source needs protection.
Moreover, the fact that oodles of subsets of the Java APIs existed for a decade, and Sun never once took any of them to court, buttresses the argument that the CREATORS of the API were not interested in protecting against reimplementation. Even GNU Classpath wasn't a proper fully compatible version of the Java APIs, it could not pass the TCKs, but Sun did not threaten it.
Yes, Google likely chose Java because hundreds of thousands of developers already spoke it. Just like Objective-C choose C and Smalltalk, because so many people already spoke it. What's wrong with building a system that will have a low learning curve and easy to transition to if it is very similar to what people already know? C# was created by Microsoft to resemble Java for similar reasons.
What I find dubious is not that Oracle might try to make a mobile OS (your argument against this is the subjective opinion that it was "awful"), but Google's claims that their use of the Java API was "fair use". Building a non-interoperable competitor for commercial licensing based on their work doesn't come anywhere near the terms of fair use. By Google's own admission, the choice to do this was an attempt to leech off of developer familiarity with Java rather than any sort of compatibility need.