in any country, all types of businesses will definitely be taxed,
Completely false. All of the countries (offshore or onshore, tax heaven or not) have tax exemptions for various types of incomes specific to the country.
so we don't need to avoid taxes, because in our country if people avoid taxes, we can be sure that the business being run is a business that violates the law, because only businesses that violate the law fear tax, because they are afraid that if the illegal business they do will be caught by the authorities.
False again. There are a lot of places with 40% tax burdens. Some people just don't want to pay stupid high rates from their perfectly legal sources of income. If you have a webshop that sells books is that an illegal activity? No. Based on where you live let's say you are taxed at 40% for your income. You don't want to pay it. Does that make selling books illegal? No.
bitcoin is not something that violates the law so why do we avoid taxes.
Because you want to keep most of your profits to yourself.