This article: Astrology, it’s no pseudoscience gives a very good overview of the three types of groups that have an argument with Astrology. The way I look at it, it’s pretty hard to disprove something you can’t understand.  In my experience most skeptics can’t really understand Astrology, and mostly succumb to contempt prior to investigation - which would get you fired if you were a detective!

Ironically, this sort of skepticism usually has Astrological indicators in a person’s chart. Someone with a lot of contacts between Saturn and Neptune or Saturn and Mercury will be very inflexible in the way they think or the point of view that they hold.  Sometime the argument against Astrology is a religious one.  Neptune rules religion, and when Neptune combines with Saturn, especially in the conjunction, square, opposition or quincunx it creates an extremely inflexible attitude - regardless of logic.

On the other extreme scientific people usually have Mercury - Saturn contacts.  These contacts allow them to have the very linear and logical thought processes needed for science.  So the next time you run into a serious skeptic - look at their chart for these indicators.  You won’t prove anything to them, but you will increase your own understanding of human nature!