To your point(and parent's), it won't be if you're never getting out of the USA nor deal with the rest of the world.

But most people moving in don't cut all ties with their home country nor never touch their passport again I think.

We travelled internationally as a family when I was a kid. No one ever mentioned our names being different.

Again, a huge percentage of the population has divorced parents, plus all the kids born out of wedlock. That is like half the population that already don’t have the same last name as at least one of their parents. Everyone who deals with the population is going to encounter this situation every day. They aren’t going to be surprised or confused by a kid with a different name as their parent.

Did you ever travel internationally along with only one of your parents? I know of many cases around the world where authorities will definitely cause you some trouble if you try to do that, even more if somehow "expected" naming conventions don't match up. At least that's how it's been in the last 2 decades.

I travel multiple times a year internationally with my toddler. She has a different last name than me. No issues whatsoever. Yes, i bring a birth cert and a letter from her mother that we can travel, but no one has ever asked for these.