If spending billions of dollars on the betterment of hunanity, for no personal gain, isn't worth of praise, what is?

It is indeed a praiseworthy endeavor.

That being said, society should not be at the mercy of the whims of billionaires. Their very existence is a grave error.

Sure, I agree that a person who spends his time trying to do good things for society is generally praiseworthy.

I praise people who do good things all the time.

But there's a massive difference between (a) praising someone and (b) having society revere per.

If we should revere anyone, it's certainly not the person whose great achievement was to spend lots more money than the next person.

Extremely rich people who are more or less retired from whatever it is that made them extremely rich in the first place often spend their twilight years focused on "philanthropy." So in general, I don't think Bill Gates should get some sort of special recognition for that.

However, what I think he does deserve some level special recognition for is what he is devoting his philanthropic efforts toward, which is making a tangible difference for the worlds poorest and worst off people. It can be credibly argued that the efforts of the Gates foundations have saved many millions of lives and alleviated a huge amount of suffering.

I also disagree with the argument that a public organization would be more effective. If by "public" you mean government-run then such an organization would almost certainly be focused on helping relatively wealthy (by global standards) middle and working class Americans. It seems unlikely that they would focus their efforts on something like eradicating polio in the developing world.

Public institutions are good and American should have more of a social safety net but I think it's probably a good thing that individual American billionaires are focusing their philanthropy on things that would be politically awkward because the people who benefit directly don't get to vote in US elections.