The point for me is that the government automatically seems to think that cash payments are for something illegal. And all of a sudden, the burden is on me to proof that it is not.

While technically speaking, paying with cash is a very legal way to pay and should not require any explanation at all. Nor should it be more difficult.

Of course, there is a limit, and I get that paying a 2 million dollar house in cash is reason to at least ask where that money came from. But 3000 dollars or 100000 are amounts of money that in my opinion do not deserve the same amount of checking.

A lot of random but legal stuff can be done with 10000 dollars of cash. And yes, sometimes you use cash because you don't want your identity known. Doesn't mean you are doing something illegal. If the government thinks it is illegal, they should open an investigation and proof it.

Instead they put the burden on you. Doesn't seem fair to me, and a limitation on my personal freedom to spend money however I like.

Not to mention, even things that are legal now, could be made illegal by governments to come, and dictators or oppressive regimes will have no problems with checking logs to see which assholes did something that goes against their values in the past. For that reason alone, governments should only be tracking the minimum amount of information they need.