What is the topic sentenc in this text?

"When people form groups of any type, a kind of organizational mind-set inevitably sets in. Although members of the group might trumpet their tolerance and celebration of people’s differences, the reality is that those who are markedly different make them feel uncomfortable and insecure, calling the values of the dominant culture into question. This culture will have unwritten standards of correctness that shift with the times we live in. In some environments, physical appearance is important. But generally, the spirit of correctness runs deeper than that. Often unconsciously conforming to the spirit of the man or woman on top, members will share the same values about morals or politics. You can become aware of this group spirit by observing how much people feel the need to display certain opinions or ideas that conform to the standards".

The above is from the book I study. The book says the first sentenc is a topic sentenc, which I don't agree with. I thick the key sentence is "Often unconsciously conforming to the spirit of the man or woman on top, members will share the same values about morals or politics", I think 'organizational mind-set' refers to th dominant culture in the second sentence. Do I understand the text correctly?