If you don't want to do business with someone from another country you certainly don't have to comply with other countries' laws. If on the other hand you do sell a product or service to businesses or people abroad you have to comply with the relevant laws of their respective home countries.

That's not a new or GDPR-specific situation but rather has been the case since pretty much the beginning of international trade.

"I got a letter from your government the other day. I opened and read it. It said they were suckers..." On a serious note though, regulation is already onerous to small (and very small) business. The last thing a rational entrepreneur would do is tie themselves up with more of it voluntarily. Unless you can present a reason to do so that is not sanctimonious.