Our
feelings are already very transparent. We
sweat, shake, and
stutter in
nervous situations. Our mannerisms completely change when we're
angry. When someone is
depressed or sad, they act introverted, are generally quiet, and often
cry. When people are
happy, they become more
outgoing,
smile more, and are generally friendlier. And the tone of our voices often changes based on our
emotional state. Everyone knows what these signs mean because of
knowledge gained from years of
observation (including of ourselves). The majority of our
communication with others is expressed
non-verbally. And I doubt we'd
lie less. After all, the best liars have found ways to control their normal reactions to adverse situations, I'm sure if we had tails, we'd find ways to control that reflex (assuming it's
involuntary).
The only sure thing having tails would cause would be tail fetish web sites proliferating the internet. ("FREE HOT 100% VIRGIN CELEBRITY UPSKIRT TAIL SHOTS" would become a common search term on Google.)
You're right, emotion is a very powerful thing, but so is sex. :-D