The "what ifs" can go on forever. At some point one has to rationalize whether or not all of this is worth it, to invest so much of oneself into another human being without first considering themselves.
The hereditary history of physical and mental illnesses that run in my family, the economic/environmental projection for the rest of this century as well as the hypotheticals that you listed tip the scales in entirety towards the costs rather than the benefits.
None of the nebulous, ineffable personal fulfillments that parents speak of have ever sounded like a basis for a good moral argument for forcing a new life into this world.
Instead let me ask, What if you, as a thoughtful and responsible person do not raise another thoughtful and responsible individual? And instead leave it to the thoughtless and irresponsible. We have to live with that too.
The second part to that is a different question entirely, and one that goes beyond just one's own happiness.
You would be surprised. Americans receive very strong lifelong messaging about how they should live their life to optimize for immediate comfort. Having and raising children definitely causes strain on one's ability to fulfill the lifestyle that has been marketed to them.