Altruism is the best source of happiness. There is no doubt about that.
If someone has a gun and is trying to kill you, it would be reasonable to shoot back with your own gun.
The Dalai Lama should not be partisan either, should remain above.
Anything that contradicts experience and logic should be abandoned.
We need an approach to ethics which makes no recourse to religion and can be equally acceptable to those with faith and those without.
Not only can I not recall my experiences in my previous lives, sometimes I can't even remember what I did yesterday.