Do you agree with this?

Not exactly generalisable I'd say

It really depends on people - attachment styles, awareness of boundaries, core values and culture, personal experiences, etc. Even if that oxytocin theory is true, regulation differs from person to person based on all those above-mentioned things/factors

Casual sex is not a new age scam. People may think like that maybe because they are unaware of the latest information about the evolution of Love in mammals and these hormones' functions. If anything is a scam, it's the fiction's definition of Love, and unfortunately, a lot of educated adults still buy that.

Love is an emotion experienced by the combined action of neurochemicals [Oxytocin, Vasopressin, Dopamine, Serotonin, Testosterone and Estrogen...], vagus nerves, mirror neurons, hypothalamus and even the primitive area of the brain (VTA) is involved. Like any other biological process, its evolution stems from survival and reproduction.

Oxytocin, also known as the love/cuddle hormone, is one of the main hormones released during orgasm - but the influx of this hormone also happens during maternal care (childbirth and lactation), bonding between couples, sexual behaviours, new social bonds, cementing the already existing bond (like meeting your loved one after a long time) etc. and steady, subtle flow on day-to-day activities such as social behaviours, social memory, trust, security, calmness, contentment and so on.

Mainly we differentiate Love in humans as Romantic and Platonic, but the hormones involved in both are the same but vary in levels.

Romantic Love can be categorised into three distinct but interrelated emotion systems. Lust, Attraction, Attachment. (These terms have a different meaning here from their everyday usage) First, two emotional systems are exclusive to romantic Love. Platonic Love is like that third emotional system but without any arousal.

Casual sex usually happens in the first emotion system. There is no guarantee that it will go to the next state. It varies from person to person how they deal with this state. Also, prostitution is considered as the oldest profession in the world.

Lust: Racing heart, sweaty palms, flushed cheeks, feelings of passion and anxiety. Crush, desire, first-sight Love, initial sexual attraction, and being love-struck can be tagged here. Not necessarily mutual, and it doesn't need to go to other emotion systems—increased levels of Testosterone and Estrogen.

Attraction: The most celebrated phase of Love, known for its ecstasy and anguish. The passionate or obsessive Love. Feel like they become your centre of the world, thinking about them all the time, heightened attention, emotions and motivation, energetic, euphoric, goal-directed behaviours, willingness to sacrifice, high empathy only for them, emotionally dependent or change of habits sometimes even values. Increased levels of Dopamine and Norepinephrine, decrease Serotonin. It's a vulnerable phase because low Serotonin and high Norepinephrine significantly impact health and regular life, like reduced appetite and insomnia.

Attachment: Companionate/Compassionate Love. The phase of a long-term relationship. The excitement of romance will be there, but relentless is lost, mainly because Cortisol (stress hormone) and Serotonin (control hormone) levels return to normal—ideal levels of Oxytocin and vasopressin.

Here is a Harvard article with details and a better illustration

https://sitn.hms.harvard.edu/flash/2017/love-actually-science-behind-lust-attraction-companionship/