I still think your interpretation is way off. There's no particular need for concentration and the character is actually not taking their time at all since no time increase is involved.
His interpretation is a little off -- there are some mechanics from "taking 20" getting mixed in with comments about "taking 10." But he's not entirely wrong. You've gone too far toward "taking 10 is a lame-assed attempt that can be used a lot." So, OK. Let's clarify.
- Taking 10 can be done without investing extra time into the task, but there must be no distractions, no combat, no stressful circumstances. You are being careful. Maybe you're not being awesome but you are keeping your eyes on the prize. This is a king calmly climbing onto a table to address the crowd. Contrast that with a condition where you would need to roll -- the king has assassins in his court, and he leaps onto the table to escape the swing of a blade. He's under a little pressure there. It's different. Such a scenario needs a roll. And in contrasting those two scenarios, we can see that taking 10 does involve less distraction and a more deliberate, careful process. Even if it takes the same amount of time. And this is probably why you've got people disagreeing with your assessment that taking 10 is doing a "half-assed" job. It's not. Again, it may not be awesome, but it is conscientious.
- Taking 20 requires extra time. It technically is similar to taking 10, in that you are not distracted, stressed, or in danger. You are also "keeping your eyes on the prize." But you are doing the task over and over again until you're certain that you've got it right. This is devotion, this is caution, this is maybe obsessive behavior. But it has its rewards. And it can't be done with something that carries a failure penalty. For example, you can't take 20 to disarm a trap, usually, because taking 20 assumes you fail before you get it right, which means the trap goes off.
And if the skill pretty much requires interacting with someone, then interacting with them really can't be considered a distraction.
Unless it carries a failure penalty or a stress point. I'd have to consider situations where you're Sense Motive-ing someone to be slightly stressful -- you're not sure if you're being lied to, the person may not be trustworthy, and bad things might come of it (whether the character knows it or not, they have to be assumed to at least
think it at some level, otherwise they'd be completely comfortable with the person and not be using SM on them).
Same for your comments about Spot. I mean, if you're Spotting, it would seem to be inherently stressful or dangerous -- you're trying to see hidden people, or see through a disguise, etc. That implies Bad Things. It might imply a failure penalty -- you don't Spot, you're dead. Ouch.
I could see taking 10 on a "fun" Spot check -- kids might do it all the time in hide & seek, where it's all in fun and the only "failure" is you miss someone and have to play the game again (oh darn). I guess I could see a take 10 in a quiet room where people have your back and you feel protected. And I could see taking 10 on Spot checks that involve a small benefit with no downside -- perhaps the king notices that his adviser has a new hand-carved staff, and he compliments the adviser on his carving skills. That's useful flattery that could bring the king up in esteem, and yet if he doesn't do it, it's not like someone would get angry or turn disloyal or whatever. It has no downside (much -- maybe if you mistakenly notice something and mistakenly compliment wrongly).
Back to Sense Motive, I'd say that taking 10 is possible. I just think you're a bad advocate for the cause. Your wording is poor, making irdeggman's position look more reasonable. And he does have points worth considering.