I still don’t understand why in legislative proceedings they still use votes out of those present rather than votes out of total membership?

I mean, what stops someone from just murdering their opposition in an evenly tied chamber in order to pass evil laws? It should be 68 votes for anything to get done, 67 or less should default to the motion being a fail. Like, what idiot made the legislative process this way? If I were to design a democratic system, it would always be majority of total membership, not this bullshit.

(But then again, if I designed the system, I would never use FPTP in the first place)