How does "lack of money can create unhappiness" downplay the effects of economic stress on mental health?
It just makes the propositional logic of the sentence clearer:
X might not imply Y, but !X implies !Y
The person I'm engaged with, and their family, had/has it even worse, and it's not hard to see the ways it affected and still affects them.
My point being, I'm no stranger to a family history of financial hardship. I'm sorry for whatever you and your family have had to endure. But, politely, screw off with the implication that the only way I feel the way that I do/say the things that I say are fruit of some privileged upbringing that couldn't possibly understand money problems.