Is outdoing monkeys while imagining free will the only way you can feel like a man?

Why does it bother people that we might be pretty similar to other monkeys (i.e. with better vocabularies, worse feet etc but no glorious fundamental difference)? Similarly what's so scary about everything being mechanistic, free will not existing, and everything being meaningless apart from the values that we make up?

If we are fundamentally similar to other animals it has no effect whatsoever on the experience of humanity that we cherish. It has always been that way, and works fine. We know what being human is like, so if monkeys are similar that should only change our ideas of what being a monkey is like. What being a monkey is like is not usually considered a pressing issue in society, so why care? Why does our societal self-worth rest on being heaps better than monkeys?

Similarly with the other possibilities listed above, if they are true, obviously they always have been and everything we enjoy is possible in their presence. It isn't like as soon as you stop believing in free will you will turn into a robot. If it's the case, you already are one, and everything you've ever loved and dreamed of has arisen from that. It's not some strange new reality.

Perhaps practically these things seem to hold different probabilities for the future to other beliefs? e.g. the universe being purely mechanistic might make Heaven seem unlikely. But you could still have a mechanistic God and Heaven and soul (it's not nearly as impossible as non-mechanistic ones). It's not the end of the world.

Or is it actually hard to hold one's own values, for instance, without the delusion that they are somehow fundamentally valuable?