I wish the public domain were the least restrictive license, but unfortunately that's just not true globally. In many jurisdictions, notably Germany, there is no public domain or the concept of a public domain doesn't match with common law countries. MIT/BSD or another permissive license is a much better choice if you value openness. [0]
In fact, the MIT license originally came about specifically because just making X public domain wouldn't fly with at least one of the X Consortium participants.
0: https://en.wikipedia.org/wiki/Public-domain_software