It isn't a person who "groups" certain people together. So, saying all cops are bad, or all women like to shop, or all teen boys are vandals, or all blacks are this, and all gays are that, etc., etc. is not collectivism, it's stereotyping. And when it borders on bigotry, then it steps over the line into racism and prejudice.
Collectivism, on the other hand, is the subjugation of the individual to the group. "For the good of the whole", or "the common good". Therefore, it is acceptable to sacrifice an individual for the sake of the group. Collectivists view the group as an entity of its own, with rights of its own. The government is the ultimate group, but cults, and some minority groups are collectivists too. Of course, it begs the question: who gets to choose who will be sacrificed for the greater good? In the case of the government, well, we know the answer to that.
Socialism and communism are built on collectivist thinking. I remember a time in school when students had to do an exercise called, "The Life Boat". Does anyone else remember that? You had 5 people in the boat but only enough supplies to sustain 4, so you had to make a choice who was going overboard, and it was based on how useful the people in the boat were. It was a lesson (indoctrination) in collectivism. It was also a subtle way to teach kids to devalue life, in my opinion.
Anyway, I thought it needed to be clarified because a lot people on these forums seem to think collectivism and stereotyping are the same thing.