Oh my god. Could you overreact any more? Is this the sort of stuff you waste your energy on? Don't you have better things to do and to think about?
ITS A NON-ISSUE.
You are among the ones overreacting
The problem now isn't that big because it is just in a few places where you can see things like twitter and facebook. However, it becomes more annoying when we go to Quicktime Player because it adds Vimeo, Youtube and Flickr. So now we have:
1. Email
2. Message
3. Airdrop
4. Facebook
5. Youtube
6. Vimeo
7. Flickr
Now imagine what will happen when others are added...we are going to need that 27" Thunderbolt Display just to be able to even use the share button if things continue to go like this. That's just complete madness.
We are not talking about something like the menus in the menubar. When menus get too much options they are divided into separate menus and submenus. This is just 1 long list without any separation, categories, etc. at all. It makes much more sense to have this as a user option where you can enable/disable it completely and select which services should show up in the share button list. You know, exactly the same thing they did for notifications centre (and by that I mean the showing up of twitter only when you've setup a twitter account as well as how NC manages the notifications). They've shown that they can do this on a technological level so yes, the current implementation of the share button is a bug or maybe even a design flaw.
I for one quite like the share button as it allows me to easily send something via email, Messages or AirDrop. I just don't like to have a gigantic list of every popular social networking site in it. It makes more sense to just add the ones you are actually using. Does it stop me from using ML? Nope, the pros outweigh the cons easily