Well, you are seeing this from one angle and failing to see it from another angle, the dangers you talked about are there just as you have described it, but did you even bother a bit to ask yourself, what it will take to buy up to 2 million or more bitcoin from the open market? Even buying 50,000 bitcoin can drive the price of bitcoin up high to the roof, not to talk of buying up to 1 or 2 million bitcoins, buying up to this mentioned about of bitcoin, I can tell you will drive the price of bitcoin to nothing less than a million Dollar, now think about what will happen when one have to spend up to a million dollars just to own 1 bitcoin, and you need like 1 million bitcoins, and remember the more you buying, the more expensive it gets.
I must be honest, I don't like the idea of the government holding such amounts of Bitcoin, but for now, I'm not too bothered about the government having that amount of Bitcoin because I see all these talks as just campaign strategies. Politicians talk a lot before they're elected and when they get elected they find out that it's not as easy as they think it is, that's if they have any plans of implementing what they said.
Let's assume the government wants to buy 2 million BTC at the current price of $64,000, that's a total of about $128 billion. I do not think such an amount of money would be released for any president to buy Bitcoin. Except it's a dictatorship, he alone doesn't have that much power. But even if he does, like you said, the more they buy the more the price goes up. It may not go up as much as a million dollars, but it will go up a reasonable amount and it would become more difficult for them to buy up to 2 million btc.