I have some friends who find that they budget much more successfully when they use only cash... they can see exactly what they have left this week or month.

Really? I find it to be the exact opposite. I budget much better when I can see what I'm spending money on rather than how much cash I have on-hand.

Youre blaming victims - if system makes it harder for people to be in control this is systems property not peoples - youre making "fundamental attribution error".

They don't think they're victims, they think they found a system that works for them. And they don't think it should be what everyone does. I had no idea that such a simple story would attract such strong reactions.

Everything else being equal. If one payment system helps you budget better, then it’s clearly better than the other.

How do you buy online with cash only? I’m in the opposite situation, I pay everything with cards and I couldn’t be happier.