I feel constantly torn over this issue because (being a gemini) I can see both sides of the argument. On the one hand, of course it doesnt make sense and it isnt real--if it was, how on earth (haha) would it work? What about the sidereal vs tropical debate? And what about the southern hemisphere? Im a twin, you see, and when I was younger I liked that I was a gemini because it seemed like the perfect sign to have, if you are a twin--and in fact, there are more twins born under gemini than any other sign--(coincidence?!?!) Conversely, the fact that my sister and I are so very different, despite our almost identical sun/moon/rising/etc signs, is good evidence against their having any validity; yet we both feel we identify with our sign, despite the differences in our personalities. Which can only mean that the qualifying characteristics of any star sign are so deliberately vague and inclusive that all sorts of people can identify with them--which is, of course, another argument against their validity.
On the other hand, wouldnt it be nice if it were true? Because, its so fun and magical. And, my life would be pretty devoid of magic, were it not for the occult (the zodiac, the tarot, and so forth). Besides, how do we know it isnt true? Just because we dont know how it would work doesnt necessarily mean it doesnt--though deep down I know, logically, it really cant (geminis are very logical, you see).
image via here