reasoning behind wanting to choose people who will make the proposal more likely to be accepted:
let's have an extreme case; say I'm like 99% sure mail-mi is resistance (I'm not 99% sure of that), and also 100% sure I'm resistance. From that I should be like "oh, cool, if I put the two of us on the mission it is very likely going to succeed!" However, I shouldn't put mail-mi on the mission because the proposal will not be accepted and so it would be pointless. I would be better off proposing a mission that has a slightly lower chance of success, but might be accepted. Since a mission with me on it from my perspective is a better mission than most, I'm willing to put people I'm a bit unsure about on my mission if it makes the mission more likely to happen.
Let's look at proposing the arch-liopoil team: arch has said he will vote against this mission because he thinks I'm a spy. So this mission would need 3/4 of the people not on the mission to agree to it. This seems very unlikely to happen, especially since TA almost certainly won't. This combined with the fact that I do not have any more reason to think he is resistance than anyone else, (and I don't think anyone else does either), is enough for me to cross that team off the list.
munch: why do you think TA is resistance?