Another argument is that death is a continuum. You can die after 80 years or after 120 or after 1,200 or after 1.2 million.
Sure, maybe if we lived 1 million years there would be problems. But it's a strawman to say that living for 1 million years is bad, so we should kill people at 100.
Honestly, (in my uninformed opinion) of all the potentially disruptive technologies, life extension is the least problematic. Disruption is worst when it happens quickly (witness AI). But life extension is not likely to happen quickly exactly because it is a complex problem with myriad causes.