Pope Pius XI, in reference to efforts of religious unity without due considerations to doctrine, warns that “unity can only arise from one teaching authority” (Mortalium Animos, Pope Pius XI, 6 January 1928, Section 9). If one fails to acknowledge that, one goes down the slippery slope towards indifferentism. As Pius XI went on to explain:We do know that from this it is an easy step to the neglect of religion or indifferentism and to modernism, as they call it. Those who are unhappily infected with these errors, hold that dogmatic truth is not absolute but relative, that is, it agrees with the varying necessitates of time and place and with the varying tendencies of the mind, since it is not contained in immutable revelation, but is capable of being accommodated to human life. The idea or practice of promoting ecumenism without agreement in regards to doctrine is false ecumenism. The union of Christians can only be promoted by promoting the return to the one true Church of Christ of those who are separated from it.” (Ibid, Section 10)Denying Catholic doctrine in the name of ecumenism or unity is clearly against the clear teachings of the Catholic Church throughout history and against the Decree on Ecumenism.
Sure, if you say so, but clearly in the clear practice of ecumenism you can twist doctrine, obfuscate it, omit it; confuse it; downplay it, pretend it doesn't matter and ignore it. As long as you don't outright deny doctrine (meaning you don't get caught doing it) it's all good.