Are beasts free? I am unsure at several points in your communication whether you are expressing your own view or attempting to paraphrase Sartre. Obviously, you are entitled to your views, and we can debate them as such. But if your post is intended as a paraphrase of Sartre, then I think you err at a couple points.
VM: [a letter opener] has no ‘essence’
“Let us say, then, of the paperknife that its essence
[l'essence]– that is to say the sum of the formulae and the qualities which made its production and its definition possible – precedes its existence” --
existentialism is a Humanism
VM: [the human being’s] nature is determined by the material from which he is made, the environment and evolution that produced him.
J: No, for Sartre, there is no human nature, certainly not one determined by material. (I may have used the word “nature” when I should have said “essence,” though many writers have treated the terms essence and nature as synonyms.) When you refer to material, environment and evolution, you may be thinking of the human
condition.