Most first attempts at writing philosophy essays fall down on this point. Substantiate your claims whenever there is reason to think that your critics would not grant them. When quoting or paraphrasing, always give some citation. Indicate your indebtedness, whether it is for specific words, general ideas, or a particular line of argument. To use another writer's words, ideas, or arguments as if they were your own is to plagiarize.
Plagiarism is against the rules of academic institutions and is dishonest.
It can jeopardize or even terminate your academic career. That is because appropriately citing the works of others indicates an awareness of some of the relevant literature on the subject. If your position is worth arguing for, there are going to be reasons which have led some people to reject it. Such reasons will amount to criticisms of your stand. A good way to demonstrate the strength of your position is to consider one or two of the best of these objections and show how they can be overcome.