You missed out on a huge objection - resources.

The planet Earth suffers from a possibly terminal condition: the number of humans has grown exponentially over millennia, and for the last two hundred years, the average consumption of resources and the average waste generation per human has also grown exponentially.

One of the first examples of transhumanism in popular culture was "The Six Million Dollar Man".

Given that the average cost of just a heart transplant in the US was over $1.6 million in 2020, becoming transhuman is going to cost a heck of a lot more than $6 million, and that cost directly translates into resource consumption.

The planet cannot afford this.

John Varley is probably the earliest and still the best writer about transhumanism, and this theme occurs in a majority of his stories in some way or another, though by no means all.

His Blue Champagne (1986) particularly stands out. I re-read it recently, I'd read all the stories before, and yet it stood up so well, and one of the stories (Tango Charlie and Foxtrot Romeo) made me try. But the title story is particularly appropriate here.