As a founder, I strongly disagree. The feedback I care about most is negative feedback. Negative feedback helps me improve.
If I don't agree with your negative feedback, next time I'll communicate better why. If I agree, that helps me address the flaws in the business sooner. I'll be grateful, not upset. Just like with user/customer interviews.
The legal risks that dissuade employers from giving feedback to job applicants don't apply for investors. If you're trying to keep your options open to invest later, I'd rather return to someone who pointed out a flaw that I then fixed which led to success.
I realize most people in general don't react well to negative feedback, so maybe this is just me, but I imagine there are others out there like me.
" If you can trust yourself when all men doubt you, But make allowance for their doubting too; "