It's situational
Let's not forget the reasons people shoot more than 3 times:
1. Accuracy limitations of paint and paintguns.
2. Bounces.
3. Human error.
4. Intelligent moving targets.
5. Wind.
6. Those stupid gremlins, evil spirits, whatever that inexplicably cause some of your shots to miss for no apparent reason.
7. Attempting elimination by splatter.
8. Hit removal, either intentionally by wiping or unintentionally by incidental rubbing against bunkers, the ground, etc.
9. Hits occuring in areas not readily visible to refs and/or perceptible to players, such as between the pods, under the pack, soles of shoes, down the barrel, etc.
If you're not allowed to make the best of the situation given these limitations, why would you want to play much at all? If you pay your money for all the firepower, accuracy, consistency, etc. that you do and not be able to utilize it to your advantage, then what motivation exists for you to continue? You'd be pissed off as hell if you walked onto a field and couldn't shoot more than 3 shots at a time if you needed to, wouldn't you?
OK, right, so your aim is a little better than usual and you land 3+ shots on target sooner than you thought, instead of the usual first couple missing and the last 2 or 3 hitting...good for you! You or they may not be aware of more than one of them hitting cause the guy ducked in, was running, etc. Only should you stop when you are aware of the guy being hit AND PULLED BY THE REFEREE. I don't give a crap what kind of holier than thou, principle above practical person you claim to be, if you think for a second that either you or I would see someone still playing on with 3 or more hits on them and think "Gee, I know he's playing on while hit and he shouldn't be, but ya know what, I've done my part. The ref will surely see that and get him out of here INSTANTLY, before he can do anything with it. I won't shoot him again because I'm a good person..." then you and reality need to meet sometime.
If someone is going to take one or more hits from me and not lift an arm, yell "OUT!" put a barrel plug in, stop moving in my direction, and stop shooting paint, you can bet every damn cent you have that I and any sensible player will put as many shots on them as it takes for them to do so. That is neither brutal nor unfair, but rightfully seeking due credit for your achieved eliminations.