Our not wanting to die is a bit of irrational behavior selected for by evolution.

Eating icecream is not rational either, it's just something we want. If someone really truly does not want to live than dying is rational. The question is, does you father want to live? I will speculate that while trying hard to convince him you labeled dying as "wrong", and set up the framework for his rebuttal.

The universe doesn’t care if you’re there or not. The contrasting idea that you are the universe is mystical, not rational.

Reverse stupidity...

The idea that you are alive “now” but will be dead “later” is irrational. Time is just a persistent illusion according to relativistic physics. You are alive and dead, period.

Again, just ask whether he want to be alive tomorrow; this is objective.

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I think you replied with pretty much the same arguments, I wrote above before reading yours. Posted for the record and for support :)