The whole point of the script is to make it so it fires when you click. The default sniping already fires when you let go so why would I want that?
EDIT:
Some errors with this script:
If you die while zoomed in, you continue to +attack, the sniper.cfg needs a -attack at the end, but so will every other class script if you change classes after dying.
If you switch weapons while zoomed you will continue to +attack, this can't be fixed unless you rebind every weapon switch key with a -attack at the end
. All you can do is right-click again to stop the firing.