Had that one soldier deviated from his path, he'd have probably caused literal chaos in the ranks.
So in the unlikely event of spotting a terrorist while you march around staring straight ahead and you have to take action, you might run the risk of causing literal chaos in the ranks?
Are you suggesting that they are only trained to march around in a highly offensive manner with no purpose to it whatsoever, and no training at all in Plans B, C, D, E, etc? No different scenarios drilled? For example, what to do if a baby's buggy or a wheelchair rolls away accidentally, straight into your path, or someone is startled by the bellowing sergeant, turns too fast, and falls onto the pavement. Or a child who didn't expect to be where he is is roared at a split second before a soldier marches straight into him...
Is this complete inability to cope with the slightest divergence from Plan A an effective way to prevent terrorist attacks?
So many of these excuses are total nonsense, utter BS.