Mass Effect 3.5B: Taste the Rainbow (Story and Ending Discussion; Spoilers!)

[Psyren]

Those are husks, not indoctrinees, though.

That's my point exactly - what Cerberus is doing is creating sophisticated husks, not just indoctrinating civilians.

Take a look at the Cerberus soldier on mars when Kaidan/Ashley removes his helmet. See the resemblance?

The problem is basically cultural. Krogan females can produce a thousand young in a single year, but nothing says they have to. During the Rebellions they had been uplifted from self-inflicted near-extinction where the viability rates the genophage inflicted were the normal survival rates, set to fighting a war as disposable infantry, and then simply given empty worlds. Now, especially if Wrex and Eve are both around, it's perfectly possible for them to manage their own populations.

That's incredibly optimistic; even Wrex on his own has very problematic leanings. ("You haven't seen how fast we can pop 'em out.") So you've basically got one Krogan - Eve - standing between the rest of the galaxy and an expansionist krogan. At best (under Wrex) they just want more room for their population to explode. At worst (under Wreav), they also want revenge. And they might want the latter anyway if there are too many Krogan for Wrex/Eve to keep in check.

Their high birthrate wasn't a problem before uplift because Tuchanka was so hazardous; they conquered the planet almost through attrition. On less hostile worlds, there'll be nothing to counter their baser instincts.