Where did you get the idea that discrimination has to be the result of an active effort? Anything that makes one group of people excluded or treated worse is discrimination, even if it is the result of an oversight.
Your second sentence is basically exactly the problem: able-bodied people are arbitrarily treated as the “default”, and others are left out.
People like you are exactly why laws like ADA were created and collectively we have decided not to just disagree with you but to pass legislation that makes it illegal for people to follow this lazy and selfish position. The first fights were over physical access and in a lot of cases it required significant reconstruction or re-architecting of spaces at great expense. The next round of fights will be over online access, where the cost of compliance is significantly less -- expect tech firms to start losing these battles now that it is much easier to attach specific harm to failures to provide accessibility.
> Able bodied people are the default because they are the absolutely overwhelming majority.
Almost everyone develops some disabilities as they age. 10-15% of the population has some disability, which is a huge group. I hope you would not argue for discrimination against ethnic minorities on the same grounds.
Your second sentence is basically exactly the problem: able-bodied people are arbitrarily treated as the “default”, and others are left out.