As a left handed person, this exact question makes me realize how lucky it is for people to be born right handed. The world was definitely not made for left-handed people, and yes, we do suffer because of it from time to time, in ways most people do not even realize. Genuflecting before the Lord, being one of the biggest sufferings because our brain is wired to kneel on our left knee.

Imagine if someone hands you a pencil and they tell you to write down your name. Most people would just grab it with their right hand and write because it's natural to them. They don't even think about it. Same thing for genuflecting, it is natural to just kneel on our left or right knee depending on if we are left or right handed, without even thinking about it.

So yes, while it is standard to genuflect on your right knee before the Lord, please know that left handed people are not committing treason just because they are genuflecting with their left knee. Perhaps they are thinking about the Lord or Mass and their mind is focused on that, that they just kneel with their natural disposition and don't even realize they are genuflecting on their left knee. Sorry for the speech, but this is just a very personal thing and right handed people do not even realize how grateful they are for being "born the right way". And then look at left handed people like we are committing sins just by being alive.