Just to be clear, at the moment, doping is not "illegal" per se in large parts of the worlds except for a few European countries.
You are bringing up good points, but to what extent it is possible or feasible to control drug use in sports is another issue. If you take all the funding away and we return to purely amateur competition, or if you make the penalty excessively large you still cannot achieve 0% illegal drug use.
Regarding your specific points (which, again, are good points on the theoretical level, but not from a practical point of view):
1) Not sure why you single out sports in your argument. Would you care about the safety of an alpinist, someone on hunger strike, a surfer on the beach who voluntarily put themselves into potentially harmful situations that have a high likelihood of death? How about a runner that runs 200 miles per week, or does intervals every day until they cannot walk? Should we not let everyone decide where they want to draw the line you are talking about? I surely would not want you to decide for me where that line is.
2) Same as point 1. Why do you care about someone else harming themselves using drugs? If it's an adult, it's on them. If it is someone under aged, it's on the parents, or the state if an orphan. For some reason it does not "feel" right for you or WADA or some other organization to tell an athlete what they can or cannot do to their bodies. They don't care if I attempt to bench press 2000 lbs do they? I mean, it is definitely harmful if that falls on my sternum.
3) This has always been the case drugs or no drugs. Being among the top countries on the Olympic medal table = successful country and/ or lot of $ spent on sports. That's why the most developed countries don't do very well relative to the most developed ones.
4) This type of destructions has already happened / is happening. Doping is already the thing fueling most performances so we have got nothing left. And to end on a philosophical point like you did. What is doping anyway? An adrenaline shot is doping, but drinking black tea purely for performance gains is not, right? What about the caffeine extract of 4 black tea bags? 5? 17? 234? How about icing - what if I use 1 ice bag, is that ok? What if I use 5? 8? 24? Cryosauna?
If the line is whatever amount of the "stuff" does not cause bodily harm then why not regulate how much and how fast athletes should train? Ban barefoot running for people born outside of east Africa.
You get the point.
Where do you draw the line between doping and why? Unless we (the global sports community) can come up with one answer to this question, it will remain impossible to get rid of the doping problem.