Understandable choice.
Still, I think it's wrong.
Preventing users from something they want to do by technical means will not change the culture.
What you will get is exactly the behaviour that you had on Twitter: People just quote anyway and do it manually. The extra effort is certainly worth the benefit.
So, essentially you are only annoying the users with some extra effort without preventing anything.
@umrath @Gargron By that logic Netflix should give you the option to download and share movies, because you can technically already do it now (legality aside for the moment). But it is not in their interest so they wont add a download button.