* Coming across as bragging
* Having people who earn less than me be jealous/envious/resentful
* Making it harder for employers to justify my salary because people will be publicly envious about it and cause a stink. This could be anything from coworkers/candidates/random people saying "well why are you paying Knaek $X and not me?" (I have experienced people harassing my employers for lesser reasons) all the way to people seeing my industry as a political outlet for their envy
* It's leaking strategically valuable information, probably more valuable than the info I would get in return (plus no solution to free rider problem)
* It might help less aggressive people negotiate a larger slice of a finite salary budget, which has a negative impact on me
And so on