1) Don't render the buttons if there are no unjoinable sites in the list
2) When present, disable the buttons by default; enable them only when a selection is made, and disable them again when everything is deselected
3) Change the 'Cancel' button to 'Clear Selections' (the button doesn't cancel anything, it just deselects all the checkboxes; was previously a input type=reset)
4) The message presented when you elect to unjoin multiple sites has some issues:
"You are no longer a participant in site <site1> ,<site2>, <site3>"
The spacing should be after the commas, not before, and the wording can be improved. New message will read:
"You are no longer a participant in the following site(s): <site1>, <site2>, <site3>"