Hmmm…
as the admin of a (very small) scanlation group, I'll feather-weigh in.
I understand your goal is to safeguard the preference of certain groups not to see their work distributed in places other than Batoto without their permission.
However, this is not the only reason groups have to choose Batoto. Death Toll, for example, don't care who rehosts our work, but we chose Batoto as our reference manga aggregator because it is the only one that allows members themselves to upload and doesn't resize pages. There are aggregators that allow for member uploads, and aggregators that don't resize, but no other one does both.
So, to reach a compromise solution, why don't you add the "chapter will be viewable by members only" option in the upload page? I don't know whether it is feasible, but it would allow groups that care about unauthorised rehosting to make things more difficult for leech aggregators, whereas those who don't care could still make their releases available to all.
I would add to do this only for future chapters, while keeping the chapters that have already been released to the date of the change available to all, as to all effects they have already been rehosted universally anyway. I suppose that level of flexibility would take quite some coding, but I see it as the least dramatic solution. And I would include some cue in the front page which allowed guests to tell which releases they can see.
(This probably has already been suggested, as it is very intuitive, but I didn't read all the comments in this thread and in any case, this comment can be viewed as adding my vote to this option.)
I'll second this idea.
Leaves the option for other scanners to have their scans spread to aggregators but frankly I'd like to have our scans be only here at batoto (assuming they don't get taken down again by DMCA >.<) because the website has always been supportive of scanlators and hasn't just been out to make a quick buck. This website has always been about scanlator choice so I think this is a good place to start and we can see where it goes from there.