Though the self-worth sentiments explored in this piece are admirable, real life is a little more complicated.
If sex is involved, serial monogamy feels less risky in terms of STDs. “Players” come in degrees so a willingness towards monogamy shown by the other person is at least a reassurance that the other person is not a player to the Nth degree ( i.e. a superficial lying narcissist). Busy older people (older than 25), who want to make the effort to get to know each other, enter into a monogamous commitment simply as a reciprocal agreement to put the time aside to actual have the time necessary TO get to know each other. Many people simply only have enough resources of time, energy, and money to only deal with one person at a time.
I’m sure others could list more exceptions to the rules you laid out here. But again, whatever the exception, your advice in regards to self worth will still be key to success. Obviously, to refrain from serial monogamy by itself, though, is no panacea.