Well, Hackett did say they'll regret it, and sho nuff, they did.
As for Wrex, in his position, I would've held the galaxy hostage as well. This is the one and only opportunity they'd ever get to cure the genophage. I wouldn't rely on gratitude and good faith to get what I want, so I'd force them all to make a choice as to which is more important to them: extinction now or possible conflict later. A debate would've been pointless, but interesting.
Ugh.
As much as I enjoy ME3's Tuchanka arc, Wrex in ME3 is a great example of how the writers in ME2 only seemed to have a passing acquaintance with the character arcs they wrote in ME2.
In ME1, Wrex's character arc is built around how the genophage is a red herring for his people's fall- that it's not the genophage that's destroying the Krogan, but the Krogan themselves. That they've been too short-sighted, too violent. It's not surprise that Wrex's death or survival depends on him overcoming the allure of a cure- of destroying Saren's facility and research for the good of everyone else.
And you know what? ME2 actually carried that forward in a good way. Wrex, if he survived, was going to change things- not by chasing cures, but by reforming the culture and focusing on breeding. The Krogan didn't necessarily like him- even his own clan has its grumbles- but they had to listen to him because he controlled the females. Don't reform, don't access the females. Less breeding, more fighting, and eventually you'd die off. Wrex's reforms were based on coercion of reproduction. Wrex's reforms were based on coercion.
Then came ME3 and the genophage cure blows Wrex's support base apart- replacing it with a dependence on gratitude and good will. Wrex- the 'mutant' by Eve's own admission- is supposed to be listened to and be able to control the Krogan firmly because... Eve likes him? Magical shamanism? Something like that.
Eve's political support depends on two things: the Krogan who agree with her ideals, and her value as a breeding female. Krogan who agree with her ideals are already going to go along with Wrex- he's the only game in town, and if Wrex can't unite the people who do agree with him, then there's no way he can unite the people who don't.
But Eve's value as a breeding female is obsolete if the genophage is cured. Wrex's entire breeding control system is obsolete. No one needs to listen to Wrex anymore because he doesn't control access to breeding. Not all the females agree with Eve in the first place- and not all the mystic shamans like Eve oppose the old bloody ways- and while Wrex can certainly claim popularity and heroism, he no longer stop other clans from doing what they want by withholding the breeding stick. He's either going to have to crush them, or tolerate them- and that includes any reluctance or refusal to go along with reforms by the Krogan who think, hey, it really was the genophage all along, and now they're free and strong again.
Wrex and Eve are either going to find themselves a well-intentioned, even respected, leader but powerless over the many different agendas of the different clans... or they're going to have to suppress the other clans by force to prevent them from escaping and acting naughty. And that will entail quite a bit of suppresion.
Seriously. ME3's sabotage choice shouldn't have been about convincing Mordin- it should have been about convincing Wrex that he was dooming his reforms. And Eve- rather than the basis of a cure- should have been the one fertile female who could use that exclusivity for power.