> Huh? Cowardly? Are you serious?
Yes, if the developer knows at least 75% of the user base needs and wants A, but still gives the choice between A and B, it is just because he is afraid of dealing with the noisy minority afterwards.
> If I am installing Ad Block, I quite naturally expect it - surprise! - to block things.
And it does block things. Whether it blocks all the things, blacklisted things, non-whitelisted things or whatever is another discussion.
> It is double more so if I am already running the AdBlock and just going through an upgrade.
A completely valid concern. The behavior of an existing product should not change during an upgrade.
> So for all intents and purposes the Sensible Thing to do is to opt users out by default from this new feature.
No, that would be an Insensible Thing, because 75% of users want the other thing.
> Now, do tell me how the hell one would let discerning users know and opt-in without throwing yet another dialog at them?
There's nothing to opt-in to, because the partial block isn't a "feature". It's now the core functionality of AdBlock.
The Hell A) The Block Everything feature could be available in happy colors in the first page of the options.
The Hell B) The AdBlock plugin blurb could say "The entire purpose of AdBlock is to block the "bad" ads [feasability of deciding badness is another discussion]. If you want to block all ads, consider installing NameOfTheAdBlockFork instead."