It seems to me that Ti has no interest in lying (and by lying I mean being in any way false to itself). Its sole preoccupation is Truth, in a very clinical sense. It does not shy away from the unpalatable or even the unethical. Such considerations are disregarded. (Whether a Ti-user actually achieves true clarity and insight is a matter of skill and not preference, of course.) That is not to say that Ti is more moral than Fe, obviously (I would hope that's obvious, anyway).
Aside from self-deception, to which we are all vulnerable, conscious lying is an entirely social process. It is an aspect of social intelligence. A social tool. It requires "theory of mind".
Fe actively asks us to lie to each other ("no, your ass doesn't look big in that", "I'm fine, thanks", "I'd love to visit your mother-in-law") in order to maintain harmonious relations (the positive aspect), or in order to manipulate someone into doing something - which may be for their own benefit, or for our own (the negative aspect). The social rituals and mythologies that Fe upholds are often riddled with deceit: Xmas and Santa Claus, tooth fairies, bogey man, religion etc, etc. Could society even function without lies? I don't know, it's an interesting question to consider. (Another one is why do we have such an aversion to lying when we rely on it to make the world go around - but that one is kinda self-evident.)
That's an interesting interpretation. Perhaps they are not. Perhaps because Ti is a pretty innocuous function in itself, Fe-users are not suspicious of it. It deals with pretty simple stuff - yes/no, black/white, logical/illogical. Not too much room for interpretation there. It's also something we are taught to acquire through elementary and further education, whereas there is an implicit assumption (Fe-bias again) that everyone will acquire Fe-proficiency without such practiced effort. Perhaps this is one reason why Fe-doms are frequently more well-rounded than Ti-doms?As a Fe-dom I don't feel that my Ti opposes my Fe, it more often seems to temper and balance my Fe, especially when I get into the analytics of interpersonal relationships. It shades and nuances the broad strokes Fe tends to make. I agree both can't be dominate; one mode will have to be subordinate to another, but they are not incompatible.
(What function was I using? )