People could equally argue that it is unfair that some children are born with all the advantages while others have none. I don't think "fairness" is a strong argument here because it is entirely subjective. What seems fair to you looks like a huge injustice to somebody else.
My parents are upper-middle class, and I've profited from their wealth all my life. My inheritance will be taxed, and I don't find that unfair at all. I was born on second base and had an advantage over others at every stage of my life; it would be fatuous to complain about an inheritance tax.
Suppose you've inherited genes which contribute in varying degrees to brains, beauty, longevity and charm. These are arguably advantages rather more significant in life than money. If there was a choice who wouldn't choose these? So should you be taxed given how you will undoubtedly profit from it? Or is it just the guy who's dumb, ugly, always ill with something and destined for a short life who's hammered if he or she happens to make some real cash?
https://medicine.yale.edu/news-article/how-genes-shape-perso... https://human-intelligence.org/intelligence-is-genetic/ https://www.technologynetworks.com/genomics/news/beauty-may-... https://pubmed.ncbi.nlm.nih.gov/23925498/
>is it just the guy who's dumb, ugly, always ill with something and destined for a short life who's hammered if he or she happens to make some real cash
I'm sorry, I don't think I understand the exact point you're making.
I follow the premise of your argument. You're saying genes are a birth advantage, just like money is. I absolutely agree with that. But I don't understand how this ends in "just the guy who's dumb, ugly, always ill" being "hammered if he or she happens to make some real cash."
FWIW, in many Western countries, healthy people are already functionally "taxed" (although it's often not technically a tax) more than unhealthy people because both pay similar amounts into healthcare but derive different benefits from it.
I also think that's good, just like taxing inheritance is.
Those unearned traits might make you more money, and you might also bequeath these traits to your kids. It would compound the injustice if you could furthermore bequeath all the money to your kids, while it would ameliorate the injustice if the inheritance were largely taxed away.