RSRH quotes Chazal who say that the Mizbeach must be connected to the ground, without any space beneath it. The idea of the Mizbeach is to elevate everything earthly and material to become spiritual. Mizbeach means shechting to eat, not to destroy. כִ י חַ רְ בְ ךָ הֵ נַפְ תָ עָ לֶ יהָ If one of the stones is touched by a “killing” sword, this makes the Mizbeach Passul (RSRH).
You become close to Hashem either by action (Olah) or passive enjoyment (Shelamim). (RSRH). We mentioned last week that the purpose of the Mizbeach is not destruction, but elevation. The Mizbeach is not a place of self-destruction, even for spiritual reasons. The Torah way is to build, to elevate, and to connect to Hashem through positive action and enjoyment, not through self-harm or excessive asceticism.