Why Collars are Sexy on Girls

Because I want to take away her agency and put her under my complete control.

Collar on her neck suggests that she is open to that. That she wants/needs you to control her. That she will not fight with you over the power in relationship and who is in charge in relationship. That she will obey all your orders and directions.

Thus, collars on girl's necks are sexy.

They give you the right cues on girl's character and her understanding of her role in the relationship. There is also a question of docile and demure she is, but it is a separate topic.

It is doubly important now, when feminism is rampart. Because of feminism you cannot just assume that a girl needs or will allow you to rule undisputed. You need something that will convince you that she is the right kind of obedient girl who will obey your every order.

You do not want to start a relationship with a wrong kind of woman and then break up because she refuses to obey your orders and thinks she is equal to you or even that she is an authority in relationship and should lead. You will waste your time and nerves. There are too many wrong kinds of girls who are influenced by feminism nowadays.