Further to my last point, I don't think it's possible at this point to say that the majority would or wouldn't want this, unless you have explicitly asked via a poll or something. I'm all for not adding any and all arbitrarily requested feature but it seems to me like this one is a basic necessity. The absence of people asking for it can't really be taken as an indication of lack of desire.
My strong suspicion is, if you did poll users of this plugin to ask explicitly if they wanted the ability to not show share buttons on certain pages I am certain the answer would be emphatically yes. Allowing people to share pages you don't want shared is a pretty big flaw. For example, one of my pages allows a download of a paid-for product. The page is hidden from navigation. Even though the download link on the page is protected by a script to prevent download without purchase, you can imagine that I don't particularly want boxes all over this page implicitly inviting people to share my download page with all-and-sundry on Facebook. Someone who couldn't write PHP scripts like this would have a problem.
I am sure there are other types of pages where site owners would not want to implicitly encourage sharing by the appearance of the share buttons on the page—password protected pages, an obvious example. Another - a market research questionnaire or poll for mailing list subscribers only that you wouldn't want to hinder people from completing by adding a password but you don't want to risk people sharing the page with those outside your target group. On others, like contact forms, it just doesn't make sense.
As BlaM4c said, I don't really see anyone being inconvenienced by this checkbox, and you can provide the ability to turn it off in the main settings page.
The reality is, and I'm not saying this just to try and twist your arm, I would have to move to a different sharing service (or different AddThis plugin at least, if such a thing exists) if I can't exclude certain pages from sharing buttons.
Thanks very much for your consideration.