>"But I'm not espousing my values, but values vital to the continuation of life."
There are no self-grounding values. You cannot objectively justify why fertility is the overriding value here, rather than, say, fairness, liberty or anything else. So yes, you are absolutely espousing your values. If you want to make an argument, make it, don't pretend it's self-evident.
Humans are a communal species, our cultures and psychology include behaviour that sacrifices our own personal reproductive chances in favour of the survival of the group, or simply deprecates personal reproduction as a priority. It’s genetic propagation by proxy, and it’s called kin selection or genetic altruism in the literature. A member of society can contribute to the survival and propagation of that society in many ways, propagating the group genome, and that doesn’t have to include through personal reproduction.
We have all benefited from the contributions made by members of past generations that didn’t reproduce, but their genes live on through their relatives that did reproduce. If all we care about is survival of the species, the best thing for all of us is that trans people get the help and support they need to leave the healthiest and most fulfilling lives possible, so that they can maximally contribute to society. I think that’s an overly reductive attitude, but that’s one way of thinking about it.
This argument is disingenuous: not only your direct ancestors contributed to your existence. You are also dependent on all of the aunties and uncles, and other members of the community around your direct line that contributed to their survival.
Every one of them also had kidneys, but that's not an objective argument for the pre-eminent moral value of kidneys.
There is an inescapable choice in choosing the grounds from which to reason out to an ethical conclusion - there is no self-evident starting point, hence the riotous confusion of moral philosophy over the last two millennia.
There are lots of conditions of the possibility of life - biological, physical, chemical - but the real point is that there is no incontestable reason to think that the conditions of the possibility of life are the pre-eminent source of moral value. Kant argued from the conditions of the possibility of understanding to moral conclusions. Sarte reasons from the conditions of the possibility of existential personality to morality. Rawls reasons from the conditions of the possibility of morality to morality. My point is, lots of people make this move, in a much more sophisticated way than you, and none is obviously better than the other - or indeed any other form of moral argument. There is no self-grounding foundation from which to reason about morality. What incontrovertible reason can you give for starting from the conditions of the possibility of life, or indeed one particular condition, rather than any other place? You can't.
What of people who were fertile but didn’t have children, through choice, medical reasons, death etc? Surely a person who is fertile but doesn’t have a child for any reason has the same net impact on the growth of population as an unfertile person (trans or not)?
Sure, but some causes of infertility are correlated and persistent.
If I'm exposed to poisons in the air or water, it's likely to happen to others as well - especially if it's at levels where it's not immediately noticed.
Many other causes of effective infertility are unlikely to impact entire groups of people across long periods of time.
There are no self-grounding values. You cannot objectively justify why fertility is the overriding value here, rather than, say, fairness, liberty or anything else. So yes, you are absolutely espousing your values. If you want to make an argument, make it, don't pretend it's self-evident.