Not sure I agree. The correct thing is to not mess with the URL at all if you're unsure about what to be doing to it. Doing nothing is the easiest thing of them all, why not do that?
URL normalization is defined and it doesn't include collapsing slashes.
Not that you can include custom normalization rules (like collapsing slashes, tolower()ing the entire path, removing the query part of the URL), but that's not part of the standard. If you're doing anything extra, the risk of breaking stuff is on you.