It isn't about knowing what's best for you, but what's best for others. So where ethics come into play is when what you're seemingly doing to yourself could act

It isn't about knowing what's best for you, but what's best for others. So where ethics come into play is when what you're seemingly doing to yourself could actually have impact on others as well. For abortion, you can claim it impacts others both ways, are you impacting a new born from having its life, or are you preventing a yet to be born child from having a troubled life, and saving family, parents and society its burden. For a vaccine, are you putting others at risk of a disease by not taking the vaccine? For bio-hacking, are you possibly creating dangerous virus or bacterias that could harm others, are you making modifications to yourself which will put a tole on the medical system if you later need assistance or special treatment if you mess up, etc. This is the same reasoning with drugs often, will your modified behavior cause harm to others if you consume them? Etc. None of this is black and white, but I think having these discussions on "what harm to others it can cause" is justified.