Perhaps it would be wise if we all agreed what the term “wrong” means.
One can do things that are “wrong” but don’t have the moral implcation of sin.
One can do things that are wrong, and may result later in situations that invite one to sin (one has free will, and does not need to commit the sin).
One can do things that are wrong and are a sin.
It is not a sin to marry someone who is not of the same faith.
It is, however, imprudent to marry someone of another faithl and the degree of imprudence my grwo depending on how committed they are to that faith. A very good person, and a very strong Catholic in my parish is married to a dyed-in-the-wool Baptist. The attend Mass each Sunday, then they go to her church for service. His two daughters are not baptized (the mother would not stand for it) and he has done his best to raise them Catholic, with no outward success to this point (the older one is a freshman in college). It is a constant source of heartache to him.
I also know couples who wee in what is called a “mixed” marriage, and the non-Catholic spouse eventually becomes Catholic.
NOTE: there is absolutely no guarantee whatsoever in any way, shape or form that the person you may be considering (since that is usually the source of these questions) will ever even consider becoming Catholic. And if a person thinks they are going to accomplish that, at least in my book they may not be mature enough yet to enter into marriage.
50 years ago mixed marriages were much more infrequent than they are today. 50 years ago, about 2/3s of all Catholics attended Mass weekly, too. Now mixed marriages are much more frequent, and we have about 1/3 of Catholics attending Mass weekly. I do not say that this is the cause of the loss of so many to the faith, but it certainly has been one of the contributing causes.