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You can also use the M-x comment-region and M-x uncomment region to comment stuff. If you use it a lot, just bind them to a convenient key stroke.

Don't forget M-; is comment-dwim which usually does... what you mean (uncomments the region if it looks commented, comments it otherwise)

This was my contribution to the SO thread! Super handy feature. I also use the - highlight block - then 'C shift -' to undo in region

and/or M-x comment-box