I flagged a question as Spam. When I clicked on the Flag link again this is what it showed me:
I raised only the Spam flag, so is all spam automatically considered rude or abusive too? What is the advantage of implementing it this way?
This seems like poor UI design, but internally spam and offensive flags are handled very similarly. Unlike other flags, they allow regular users to take direct action without moderator intervention. If 6 spam or offensive flags accumulate on a post, the post is deleted, locked, and the user receives -100 reputation and the information is fed into the automatic anti-spam system.
I'm not sure, but I believe selecting "spam" vs "offensive" changes how the anti-spam system handles the information, but besides that, there's little difference in how they work internally. They are only different from a user experience perspective.