I hate leaving a group to add a new one...
Add that to the fact that I am a citizen of a literal micronation and you can only imagine how many groups I'm in just related to that. Toss in the landowning groups that I also have to be a member of due to my land holdings and there's another chunk gone, poof! I want to be a member of my friends groups or just groups that seem like too much fun (like "Ferret!"), but I can't. If you have the same problem that I do, you can go to SL's Jira system and vote on it HERE.
If you've never used it before, it's easy...When you're in the topic/issue, look in the left sidebar. Under "Voting", click on "Vote for it". You'll be taken to a log-in page if you aren't already, which is simple...the same usrename and login for the main SL site.
It's that easy!