I totally agree with you.
I've never understood why some Saints fans have referred to Ibrox Stadium as Greyskull. As well as the valid point you've mentioned about Greyskull being the home of the "good guys", Greyskull actually looks green as well. Sometimes I've thought perhaps Saints fans called Ibrox Stadium "Greyskull" because it looked green in some strange form of irony but I never quite got it. Surely if any stadium looks like Greyskull castle with the huge green stands it would be Celtic Park? Again, though, they aren't good guys either and not fit enough to live in He-Man's Castle.
I've just clicked on your link to Wikipedia and I now see that it's all Kirsty McCabe's fault.