The only time that I have a problem with it is when the tag stealer set back doing nothing while I engaged the enemy and just as soon as the fight was over ran his little legs off to pick up the tag that I earned that's not more than 10 ft in front of me. That's just being a douche. Now if you pick up a tag that's across the map from me or even grab one on your way through an area by happenstance then I don't have an issue with it. But there are some guys out there that never go for kills and use a speed class to make sure that they can get to your tag before you can. Those guys are cheap players that aren't playing for the win but rather playing to boost their personal scores. Heck I've even left my own tag for a guy that needed it to finish getting a scorestreak if he was smart enough to let me know about it but I've got no love for the guys that go out of their way to steal your tags just as soon as you make them.
I don't have an issue with people going after tags that are out in the open. What I have a problem with though is seeing someone physically watch me pick up 3 kills whilst they sit in cover then proceed to run out just for the tags. This affects me in 3 different ways.
1) It ruins my chances of kill streaks that could seriously impact the game. I only get 25 points instead of the 100 and more often than not the person grabbing the tags is running a Care Package or Hellstorm as their HIGHEST streak. I run Lighting Strike or even a Stealth Chopper as my lowest and always have a VSAT picked. I know which will be more valuable to the team effort.
2) More often than not, they keep buffering me around as they are running directly into me on the same route for the same tags. This means I struggle to remain accurate and/or get killed as a result.
3) It also leads to the other team getting free kills. If I pick up the kill(s), I'm much more likely to know where enemies will be as I know which direction I travelled for the kill(s). A lot of people start running out into the middle of nowhere for the tag confirm and I sit there shaking my head as I know the enemy will pick them off with ease.
If you're running hard and stumble upon tags that you are much closer to than someone else, fine, pick them up. No worries at all and just laugh at people calling you out as a tag thief.
Communication can be so important in KC. If you have someone 1/2 confirms away from a useful streak for the team then give up your tag confirms and let them get them. Equally, if you're in the same position close to a streak, call it out. Most genuine KC objective players are more than happy to help for a team win.
It's those selfish 'every tag is my tag' people that annoy me. As long as I can see a team-mate actively looking at the situation and doing the best thing for the team, I'm cool with it.