I agree on a scientific basis that there's nothing really there for a reason for existence, but the morals just don't work for me.
It sounds as if it's an excuse to be stuffty to people.
Whether you think that life has a true-purpose and meaning or not doesn't mean that you should condone violence and murder.
Because when you get down to it, scientifically, we don't have an ultimate purpose in life, other than to live.
We're here to survive and continue to exist.
My DNA codes for proteins designed to allow me to survive on this earth and pass on my Genetic Information to a next generation so that they too can live.
So, it is my moral prerogative to ensure the survival of members of my species to allow for a greater chance for my genetic information to be carried on and survive.
And for that reason, I have morals and I know that it is best for myself, my future and my species that I do not murder. I do not injure my fellow humans and I live as peacefully as possible with them.