mass-effect-galaxy replied to your post “This playthrough is A Lot.”
So, what was Shepard's motivation to sabotage the cure?
There were two (connected) motivations described. The main one was that Shepard believed the Krogan were too dangerous to risk curing. The side motivation was that sabotaging the cure meant the Salarians would help in the efforts against the reapers.
The main point is kinda understandable if you buy into the idea that the Krogan are an irreparably violent species who will inevitably cause a second Krogan Rebellions (not something I agree with, but it is definitely hinted that there are many Krogan who wouldn’t be opposed to striking out against their former oppressors, so you could make the argument).
The secondary point is only acceptable (in my view) if you don’t take into account that the cost of the Salarians’ help is betraying the trust of everyone you know and care about, let alone allowing the genophage to continue and having the blood of thousands of stillborn krogan on your hands. So, not acceptable in my book.