The proper warning for each prohibition is also spelled out later. The Creator spoke to the myriad of Jews assembled the first two commands. Hashem wrote the first two tablets whose pieces are kept in the ark with the second set inscribed by Moshe. The 'Erev Rav' of nations around the world were also witnesses. Displaying the tablets testifies to the revelation at Sinai.
Human life is sacred.
Better an idol worshipper than an atheist. An idol worshipper can be grateful for being created, and acknowledges a superior being. Yet he is equated with a murderer. So Hammas, Hizbolah, etc. are associations of idol worshippers. The afterlife is learned from the written torah.