What Can Happen in the Course of Vulnerability Disclosure
insinuator.net
insinuator.net
Alice says "hey, we'd like if you toned it down a bit, but otherwise appreciate your research. Good luck with your presentation." Bob then releases all of Alice's source code in his presentation. Alice sues bob, but oops, she said "good luck." No dice.
Independent of whatever is "right" or "just" or "reasonable", there are more downsides and potential liabilities to saying "yes" than saying "no".