Siege is a totally different ball games. Of course the spawn point for defece is the spot they are trying to defend. If they let you get to close and you sk them well thats their own fault and problem.. its part of the game.
Peoples objections are when in large fun games, people intentionally sit @ at a spawn spot and forget giving people 5 seconds... they mow them down as fast as possible... its not always possible to play on a team where guys will work with you to defend your spawns etc...
There is a balence between winning, and keeping the enjoyment. somtimes the balence is a little... well unbalenced
Flanking is one of the best and most effective strategies in this game, and in any tatical situation like this... thats not the issue here.