Walts decision in Phoenix is actually stupid.
Spoilers for Phoenix S2 Ep 12 below
Since titles cant have plot points I mean the decision to let Jane die was actually stupid not cruel of Walt. Gus had just told Walt off for being with a junkie and how theyre unpredictable, Jesse said he wont hear from either of them again, also Walt didnt need Jesse as in his mind he was done with the whole Meth thing after this. Jesse leaving on his own accord absolved Walt of guilt while also leaving him solo for future. There was no reason for him to let Jane die even in that mindset.