In the Catholic Church, the belief that one religion is as good as another, and that all religions are equally valid paths to salvation, is a condemned heresy.
ENCYCLICAL OF POPE PIUS XI
ON RELIGIOUS UNITY
Certainly such attempts can nowise be approved by Catholics, founded as they are on that false opinion which considers all religions to be more or less good and praiseworthy, since they all in different ways manifest and signify that sense which is inborn in us all, and by which we are led to God and to the obedient acknowledgment of His rule. Not only are those who hold this opinion in error and deceived, but also in distorting the idea of true religion they reject it, and little by little…
This undertaking is so actively promoted as in many places to win for itself the adhesion of a number of citizens, and it even takes possession of the minds of very many Catholics and allures them with the hope of bringing about such a union as would be agreeable to the desires of Holy Mother Church, who has indeed nothing more at heart than to recall her erring sons and to lead them back to her bosom. But in reality beneath these enticing words and blandishments lies hid a most grave error, by which the foundations of the Catholic faith are completely destroyed.
WAS PIUS XI wrong to be concerned would Pius XI believe that some ideas that are placed under the banner of Ecumenism could be seen as Indifferentism. Or does the different times we live in no change things.