You forgot plenty of other exceptions. The fertilization may not be successful. The zygote may fail (or never have a plan, being in-vitro) to implant. And because there are so many exceptions and unknowns at this point, it may not be the beginning of a “new, unique, and distinct human being.” There’s simply no way to know whether it will or will not become a human being. It only has potential. Similarly, there’s no way to know whether an individual egg or sperm will ever become a human being. That is why I see them as equivalent, separately or together, and picking any point in time before, during, or shortly after is entirely arbitrary. You think that it is a natural point of distinction that “makes the most sense,” but it does not make any sense to me for the reasons mentioned here.
It’s not so different. You either consider a fertilized egg to be a separate human life worth protecting or you do not. Any laws that attempt to protect life at conception would have to make an explicit distinction. I don’t know whether existing or proposed trigger laws do this, and I have serious doubts.
So you’d force someone to get it implanted? Or force the government to pay for storage in perpetuity (people die, corporations dissolve)? Neither is realistic, so your idea would most likely make IVF impractical.
Your aunt had 3 kids through IVF, which statistically implies that she’s either extremely lucky or she had a few miscarriages along the way. Takes a hell of a woman to go through it so many times. But I also have to wonder why she chose that route over adoption. By the way adoption is very difficult in the US – nobody is giving up newborns, so most children in need of adoption come from difficult family situations (like child abuse or parents losing rights for other reasons) or have special needs (health / disability). Takes a huge heart and lots of money (or time) to care for them. And the patience knowing that when they’re teenagers they’ll inevitably tell you “you’re not their real parent” 