People are baptized Christians; is why RCs understand any baptized Christians coming into Catholism need not be baptized again - there’s no such thing as a “second baptism,” nor do RCs see any need for it.
Actually, your statement is to much a generalization, as whether a proper baptism took place is a matter of judgment.
Thus the CE (1907) states, Practically, converts in the United States are almost invariably baptized either absolutely or conditionally, not because the baptism administered by heretics is held to be invalid, but because it is generally impossible to discover whether they had ever been properly baptized. (www.newadvent.org/cathen/02258b.htm#VII)