Along the lines of @AnonStoleMyPants – the trouble with longtermism and effective altruism generally is that, unlike more established religion, it’s become en vogue specifically amongst the billionaire class, specifically because it’s essentially just a permission structure for them to hoard stacks of cash and prioritize the hypothetical needs of their preferred utopian vision of the future over the actual needs of the present. Religions tend to have a mechanism (tithing, zakat, mitzvah, dana, etc.) for redistributing wealth from the well-off members of the faith towards the needy in an immediate way. Said mechanism may often be suborned by the religious elite or unenforced by some sects, but at least it’s there.
Unlike those religions, effective altruism specifically encourages wealthy people to keep their wealth to themselves, so that they can use their billionaire galaxy brains to more effectively direct that capital towards long-term good. If, as they see it, Mars colonies tomorrow will help more people than healthcare or UBI or solar farms will today, then they have not just a desire, but a moral obligation to spend their money designing Mars rockets instead of paying more taxes or building green infrastructure. And if having a longtermist in charge of said Mars colony will more effectively safeguard the future of those colonists, then by golly, they have a moral obligation to become the autocratic monarch of Mars! All the dirty poors desperate for help today aren’t worth the resources relative to the net good possible by securing that utopian future they imagine.