Many people don't endorse anything similar to the principle that "any argument for no more of something should explain why there is a perfect amount of that thing or be counted as an argument for less of that thing."

E.g. thinking arguments that "life extension is bad" generally have no implications regarding killing people were it to become available. So those who say I shouldn't live to be 200 are not only basically arguing I should (eventually, sooner than I want) be dead, the implication I take is often that I should be killed (in the future).