Wow. Not that you were waiting with bated breath for my approval, but that was one helluva post Danjanou.
Legionaire: The way I look at your question is this: If you ask a soldier if he's shot at/killed someone, he's kinda stuck. If he answers 'yes', you look at him differently. You might always see him as a 'killer', and not one of your buddies. You might view him as less of a man, maybe more of a man. You will almost certainly view him as being different than you (assuming you have not done the same). That would be a bad thing.
If he answers 'no', some might think that he is somehow less of a soldier for not having done so.
In either case, it's a highly personal question and one that is generally never, ever, asked. As well, whether someone has or has not is almost completely a result of circumstance, and not a result of the man's personal abilities or tendencies. If put in a situation where firing on the enemy is appropriate, I would hope that all soldiers would. Further, I would also hope that the soldier would not merely fire at the enemy, but actually hit him. So your question is not 'have you shot at anyone', it's really 'have you killed someone'. I'm sure you can see how that would be innapropriate.
Not having been in that situation myself (there, you got one response), I am speaking based on my perception of my fellow soldiers.