I guess we'll have to agree to disagree on the level of difference between giggling at Kirk or decorating his shirt with "Kirk is a Jerk"...
The difference is where the impetus comes from. It's easy to program a nonsentient computer to speak or behave in a seductive manner, even today; a lot of Internet porn surely depends on it. We know for a fact that the will
behind that change in the computer's behavior came from the Cygnetians who reprogrammed it, so it does not constitute evidence of will or cognition in the computer.
But in TPJ, the premise is that the impetus comes entirely from the computer itself. What happens to it is depicted as a malfunction, not a "possession" by some other entity. So it's not an equivalent situation.