It can seem like all brownnosers are alike. They're certainly working from the same playbook. Plus, it's hard to look beneath the surface when your skin is crawling.
The basic behavior is the same, and there are common threads between types (for instance, brownnosers tend to be insecure, and "getting ahead" is a top priority), but motivations and ethics can differ from suck-up to suck-up.
First, there is the person who is so dramatically insecure in every way she thinks the only way people will like her, help her, support her or promote her is if she constantly flatters and agrees. She probably flatters everybody, not just the boss.
There is the brownnoser who uses obsequiousness to hide the fact that he is incompetent at his job. This is about self-preservation: Ingratiation might draw attention from sloppy work, laziness and/or inaptitude.
There is the suck-up driven by ambition. Likely competent, she uses flattery as a back-up plan to push her up the ladder in case her good work fails to be noticed.
Each type of suck-up may or may not pose a risk to other employees, depending on ethical make-up. If he puts down his peers in the process of building himself up, he poses a danger to his co-workers' reputations and perceived job performances. Malicious or not, though, there is one essential element of success that always suffers -- morale.
In the face of perceived injustice, a workforce can suffer a general sense of disgust, frustration and impotence. Low morale can make a workplace depressing and unproductive and is one of the best reasons to take action against a suck-up of any type. And while action that hurts the brownnoser might seem an appealing course, that's not always the wisest way to go.