People go out, have short relationships / flings, one night stands without any intent other than have fun. It's fine. Let people have things.
What if there is a diamond in a pile of garbage ?
If someone legitimately enjoys casual sex AND has no baggage OR some kind of dark triad trait.. is that sort of person common, or rare?
As for the act: If there's no harm to anyone, its great. ON that light, casual sounds logical. But is your own body just another playground ?
Throughout history, there are numerous records of temperance being a virtue and hedonism being a vice. Coming from all sorts of corners.
Its not as clear cut.
I'm making no assumptions _about_ intent.
I'm saying whether it's a "red flag" depends _on_ intent (which is then assumed to be known, at least internally by said person(s)).
I'm making no correlation between having causal sex and the attempt to establish a long-term relationship, I don't know how I could more explicitly define those as two different goals.
Maybe if I write it in a more simplistic (albeit, less precise) way:
* Many relationships may likely a red flag in a person who's seeking long-term relationships (ie, they're trying and failing very much, they're probably not a very good partner, or has very good judgement).
* Many relationships are not a red flag in a person who's not seeking long-term relationships (they're doing their thing, and all is good, as long as you're aligned with that).
Like, having 23 partners because, excuse my french "Elle voulait simplement baiser à tout va" is just fine (tm), they did what they want, and that tells nothing else about them that the fact they did what they enjoyed doing.
On the other hand, if they were looking for the one true love and thought they'd find it in 23 different people, it may reveal something else about them..
That they prefer a type of partner which does not align with their goal.
Or that they are a terrible judge of character.
Or that they are easily manipulated in general.
Those may be red flags in their own right, if those traits are undesirable to you.