Philosophically, is non-source available brews something we want, or should all brews have their source available?

I think it makes sense for users to prevent others from cloning their stuff and claiming it as own by the click of a single button, lol

So long as we don't frame the option as being total protection, because it isn't,

Should be part of #1908

This is somewhat complicated... There are currently two access types, share and edit. The new Brew Locking feature I've been working on will block any attempt to access a "locked" brew via any method other than edit. However for this feature, we'd need to differentiate share based on the calling page: perhaps something like view (for /share) and source (for viewing /source, cloning to /new, and so on).
It's not impossible and probably not the most difficult feature in the world to create.

Account wide protection, however, is a bit trickier. We either need to add a check against the User's account wide settings (which, specifically, don't exist at this point in time), or come up with a way for the User to update multiple (or even all) brews at once (which also does not currently exist).
To be clear, I think both options will need to exist at some point in the near future. Account checks probably makes more sense; in that it has a much smaller potential DB impact than users mass updating their brews.