I can’t speak to step-children, but my daughter is adopted and I see no difference as a parent. I agree with you that it’s rude to highlight the distinction.
Problem is, IMHO, too many people focus on the biological connection. On “having a baby”. This is why so many people struggle so hard and spend so much on IVF or other biological alternatives if they can’t get pregnant the standard way. It’s all about giving birth and having the baby.
To “have to” adopt is seen as an also ran. A consolation prize by some.
My wife and I encountered a weird occurrence of this when we chose to adopt. The adoption agency placed us in a group with other perspective parents. At our first meeting, every couple shared their stories of anguish and heartbreak as they tried again and again to get pregnant with no luck. They all finally admitted defeat and decided to settle for adoption.
When we shared our story, of how we just chose to adopt and had no idea if we could get pregnant, many of the other couples became mad at us. Shocked that we wouldn’t at least try to get pregnant first. One couple asked the agency if we could be removed from the group because it was so upsetting to them that we were squandering our (presumed) ability to get pregnant.
See, I think if we all shifted our focus to the idea of “becoming a parent” instead of “getting pregnant”, the ‘how’ of it all would matter less and your children would simply be your children regardless of how you came together.
But what do I know?