That line of logic bothers/infuriates me a lot in multiplayer games. You see this type of reasoning employed a lot to justify really crappy game breaking actions. "Spawn killing is a valid tactic, you have to stop them from doing it!", "Spending the entire game sniper camping is valid, just don't be a target", etc, etc.
It's an easy excuse to justify basically trolling the hell out of other players. It's not "playing a game" when you're actively crushing the enjoyment of another person for your own desires to win.
I think there is a difference between stalling and stalling. If someone stall agains a fast team for a round or two (lets say is turn 7 but he waits untill turn 8 to score) I think it's a valid tatic. But if a team is completely dominatet and someone stalls for maybe 5 turns I don't see the point. Most teams can score a second time in 5 turns and it's far less frustrating for your opponent.
I think stalling to a certain extent is fine. Again, Mafia's stalling on me was fine. It didn't bother me. I thought he could have scored more if he'd been aggressive, but hey, that's his choice.
If someone got the ball on turn two at the endzone, and then sat there for the rest of the round? I'd have a problem with that.
As you stated though, I was more or less saying the defense "Well, you're just not good enough to stop it" really chaffs my gears.
The things Hawk listed above leads me to a rule I set for myself when I started getting more competitive with this game. If I camp, I only do it for 1 turn (unless the team is a 1 or 2 turn TD, and only if I actually need to for victory). Otherwise I have two goals: to have fun (which comes and goes, honestly) and to make the game ultimately more exciting to watch.
Something I've come to notice since I've been playing as Nurgle is they're very BORING to play. The only times my games have been exciting is when I score with my Beast, or I perform a miracle double dodge and pass with my rotter.
My point is I try to play like a game I want to watch. Sometimes I lose, and that sucks. But oh well. I had more fun and had a more enjoyable game.
What I've found, is I get more aggressive the better the team I'm playing as. It's hard to explain, but like...Halflings, I never had any expectations. If I scored, I was overjoyed. But with Chaos Dwarves in S1 and now with Undead in S3, they're good teams. So I guess I'm putting internal pressure on myself to live up to how good they are. It's not my team failing me, it's ME failing THEM, which aggravates me. I'm starting to think that, along with health issues is why I broke down S1 and nearly quit, while I loved S2. Shoulda went with Gobos.
I also try to play in entertaining fashion. I don't know how many times Rodzaju and others IM'd me post-game telling me that I could have done this or that or whatever, my reply was always "You gotta have STYLE~!".