Of course they shut down lemonade stands. Especially if you tried to run a daily lemonade stand out of your front yard, staffed by people who don't live there.

And yes, authorities do shut down lemonade stands: https://www.google.com/search?q=authority+shut+down+lemonade...

I think it's silly, but there it is.

right, someone has done it somewhere. I knew that when I made the comment, it doesn't change the general applicability of the point.

They're legal because the government has not decided to make them illegal. If the government decides that your lemonade stand is a danger to public health, or that your stamp collection is a national patrimony and cannot leave the country, it will make new laws that enforce those decisions.

Or, they're illegal, but the law isn't enforced, so people feel they are legal.