You can chamber block a couched lance. You may also notice that when couching, it's very easy to get out of the way if you're paying attention. If you're not, then of course a couched lance is going to massacre someone who isn't ready for it. It's being braced by a 200+lb person, riding a horse that at the time was 800-1200 lbs, galloping at least 15-20 mph. The whole purpose was to destroy things.