Vermeersch was no modernist; he was vehemently opposed to modernism. And he was no idiot.
Well, in this case, he was either a moral modernist or else was in fact a bumbling idiot, because the principle of primary and secondary ends is clearly taught by Pius XI, and it's clearly taught that the two ends cannot be inverted. He also clearly stated what those.
Pius XI defined the primary ends of marriage and the secondary ends of marriage.
Pius XI clearly stated that the two ends could not be inverted.
Those principles are clearly understood by all Catholic moral theologians, because on them rests the entire moral theology regarding the 6th and 9th commandments.
In context, in that statement, he was talking about the specific context of a scenario where only the secondary ends were available, and clearly stated that in that case the primary ends would not be subordinated to the secondary by merely not inhibiting or interfering with the intrinsic nature of the act. He said in this situation not inhibiting the act sufficed because thereby would be avoided the inversion of the ends.
And the deviants on this forum who continue to push, promote, and condone Natural Birth Control (very possibly because they practice it themselves), you will answer to God for this ... as I'm sure Pius XII had to answer and very possibly is still answering, and will be answering (for this and for a fair number of other things).