Saying casual sex destroys your ability to form meaningful romantic relationships is like saying that talking to a stranger at the bus stop takes away the meaning of your friendships.
Without commenting on the wisdom, or lack thereof, of casual sex, this is simply an awful analogy.
Because unless you’re polyamorous (a lifestyle I am neutral toward though I tend to find some its champions a bit tedious) there is a presumption of exclusivity in a committed romantic relationship. There is no such presumption in platonic friendship. Also, sex and talking to strangers are two wildly different things, with different emotional and psychological components. Also, talking to strangers can commonly lead to friendship. The hit rate on casual sex is a bit lower nowadays, I’m given to understand.
So the analogy, teased out, looks like this:
Saying that casually (ie counter to the idea of commitment) engaging in behavior commonly reserved for committed romantic relationships and replete with attendant physical, emotional, and psychological ramifications, damages your ability to forge those committed romantic relationships is like saying that casually engaging in behavior with usually very slight emotional impact and commonly understood to be the gateway to a deeper but entirely non-exclusive relationship damages your ability to form the very kind of relationship that is often formed through just such an interaction.
In other words, “saying that -1 negates 1 is like saying that 1 negates 1.” No, it’s not like saying that at all, because the nature of the antecedent principles is different.
Here’s the thing, if people want to do casual sex, cool, knock yourself out. But please don’t elevate it to the level of exalted (and implicitly more evolved or correct) choice. It’s a choice. Not always, maybe even not often, the better one, though sometimes it is. But in the end it merits no more defense than monogamy, abstinence, or any of a number of choices.