The first reason why it's not allowed to bring a lot of cash is to restrict money laundering. That is also a reason that there is no bigger denomination of bills within different countries. This depends on the value of the country's currency as well. You answered this already. I'm just making another point about what they are doing to prevent it.

You cannot fully impact your country of origin's economy unless you have the majority of it. It's not going to be beneficial for the country and exchange your current money, too, unless you have big stacks again. The same goes for any other kind of asset. If you are talking about small amounts, it isn't imperative. It's not the main reason it's being banned, but it could be a part of it. The majority is still that those countries that do not influence Bitcoin don't like the idea to have their citizens using this non-taxable thing if not declared.

I'm not sure how Bitcoin could destroy the economy with your reasons, but what I can see is that it's improving the financial aspect when Bitcoin was born. It influenced cashless transactions all over the world with a click and made it easier. It's the start of a great improvement.