You have a valid point, what's legal and what makes common sense it not necessarily the same.
The warning lights are explicitly mentioned in the preflight check list, and if any item from the preflight list is not a positive check, you cannot just fly and do nothing about it. Also, the EPs reference the MR temp light.
Part 91.213 (d) (4) states: "A determination is made by a pilot, [..], that the inoperative instrument or equipment does not constitute a hazard to the aircraft."
This leaves some play for interpretation, but I would argue a non-functioning MR temp light is a potential hazard to safe flying.