People that shit on the Market St sidewalk in broad daylight are not doing so because they were looking for a restroom and ran out of time. There’s a little more going on.
Why bother trying to have dignity if the world doesn't want to let you have any?
(Of course it's not so simple.)
I don't see how a homeless person would be able to use an establishment's bathroom more than once without being kicked out. Some places even hired security guards to stand outside of bathrooms and check receipts before allowing you to use them.