A code of ethics seems like a tall order. You'de never find a group that fitted you! Too many variables. I couldn't even find a partner like that - let alone a group. Successful marriages seem based on basic similarity with compramises, not total agreement in everything. Then again I'm single and not a member of any druid groups - so I'm on the outside looking in, as it were. I'm the last person anyone should listen to.
Personally, I have no problems with a code of conduct for group memberships, though. It's a basic requirement of membership to most things, for all the obvious and sensible reasons that you never should have to say - but say anyway because experience has taught you better.
When there's trouble - having a code of conduct makes the mediator's job a hell of a lot easier too.
Accepting and being accepted by a Druid group is easier on both sides if there is a code of conduct to refer to.
If a person does something which reflects badly on a group, a code of conduct not adhered to can exhonerate the group, as long as they act upon the infringement, and not cover it up. Likewise, it can be a nail in the group's coffin, if they let it.
It doesn't stop me being a druid if I forgo druid groups, and their individual codes of conduct.
It doesn't mean I don't have a personal code of conduct of my own.
It just means people will have to ask if they want to know.
Personally, I embrace other distinctly druid and celtic practices, where I can find them, and where they seem to make sense as just and right in today's world. So like most, I expect, the Triads and Brehon Law are my area of research when looking for druid distinctiveness within my ethical beliefs.
So yeah, I would say a basic code of conduct would be as good thing. For a group. Get one that kicks ass and it will probably become widely adopted, like the Druid's Prayer. Eventually though you'll get the "so and so isn't a real druid because they don't use the code, the prayer, whatever...." scenario. So asking if you should have one, and be spreading it beyond the group, is also a good question to ponder.... If it were me making a suggestion for a group, I'd put it to them to copyright a code of conduct to just that group, stating it is the basic code of conduct of your group only, to save forcing the issue on others... but that's just my opinion.
And the stress of wondering what was the best way to vote is probably why I'm not in a group. Easy to talk the talk if you aren't walking the walk, I guess. But those are my thoughts, looking in.