It is more complicated than that. This is all about what today's society expects and how people conform to those expectations.
I believe a better analogy would be "I draw a picture, make a large number of copies, and leave them in a public building. Do I expect that people walking by won't pick one up?".
The answer depends on how hard it is to make the copy, where in the public building the copies were left, what notices were posted at the door of the public building, what the passer-by intends to do with the copy, and whether the original producer is deprived of anything.
If each copy was an oil painting on canvas I suppose you might reasonably expect a passer-by to leave them lie. Especially if that passer-by intends to pick up the entire stack and sell them on a street corner. After all each copy cost the original artist something in materials and time, and I would be depriving the original artist of those costs.
If each copy was a photocopy, I can't see anyone assuming that they can't pick up a copy. Material/time costs to the original artist are minimal, so as a passer-by I won't feel that I have deprived anybody of anything by picking up a copy to take home and hang on my wall. In today's society a stack of photocopies in a public place implies they are to be taken.
Of course, if I take that photocopy and publish it in my newspaper in order to sell more newspapers, The original artist might have cause to object, as that act isn't generally supported in today's society.
In GitHub, if I put some sourcecode there, and make no attempt to protect it with password or license, I don't feel today's society would not allow me to object to people downloading it for personal use. But if I include it in a project for sale, I should take care to read the licenses and get the necessary permissions.