Earlier quoted context omitted.
The argument against that is that with the collapse button so close to the vote arrow, we would be guaranteed to get misvotes, especially on mobile. The undo vote feature would no doubt help with that some, but only so much.
The HN app I use lets you click anywhere in the heading line to collapse/expand. Could you do the same here?
Both the username and the date are clickable links in the HN interface (to the user profile and the comment itself, respectively).