The problem with allowing one or two or three drinks is, where do you draw the line? Too many people will use that as an excuse to consume to excess. It isn't whether a glass of wine is good for you or not, it is that a line had to be drawn somewhere, and drawing it at ZERO alcoholic beverages avoids a lot of trouble down the road. Same with caffeine. Is a small cup of green tea bad for you? I don't know. But again, a line had to be drawn somewhere and it was easier to just draw it at zero tea or coffee.
Keep in mind that this does not apply to herbal tea, it very specifically applies to caffeinated teas made with the leaves of the tea plant.
What about soda? You have brominated vegetable oils, preservatives, caffeine, and other harmful ingredients. 5 hour energy drinks, energy drinks with massive amounts of caffeine - why does the church allow this?
The answer is because it is not feasible to micromanage a list of what can and what cannot be consumed. The church would have to evaluate every single beverage and food that came out and maintain a huge list of what we can and cannot consume. Instead of doing this, the line is drawn at alcohol, coffee, caffeinated teas. We are left on our own from that point forward to decide for ourselves what to eat and drink. We are counseled to avoid harmful and/or addictive substances, and a while back there was even a talk published on the dangers of energy drinks. But the church is not going to start dictating to the members what they can or can not eat and drink. Doing so just isn't feasible. The line has been drawn, and it is up to us to figure out where to go from here.
The church never said it was the caffeine that was the cause of the prohibition against tea and coffee and in fact the church has never taken an official position on caffeine consumption. This is what the church has said officially:
"With reference to cola drinks, the Church has never officially taken a position on this matter, but the leaders of the Church have advised, and we do now specifically advise, against the use of any drink containing harmful habit-forming drugs under circumstances that would result in acquiring the habit. Any beverage that contains ingredients harmful to the body should be avoided."
(LDS Church, Priesthood Bulletin, Feb. 1972, p.4)
The church handbook likewise says nothing about consuming caffeinated beverages.