Of course Pope St. John Paul II is absolutely correct. No circumstances can make an intrinsically immoral act licit. And the Catechism is also absolutely correct. No good intention can make an intrinsically immoral act into a moral one.
When I said “intention matters” in my above article, I was referring to those who intentionally rendered their conjugal actions infertile (by use of contraception, surgical sterilization, etc.) as opposed to those where are infertile through no intent of their own due to age, illness, and so forth.
When it comes to manual or oral stimulation of the genitals, we seem to disagree over whether that alone constitutes “an unnatural sex act.” I would say no, and I believe most moral theologians would agree. To suggest otherwise would render the conjugal act into a rather mechanical “insert Tab A into Slot B” exercise, which seems to place needless limits on the expression of spousal affection. I am unaware of any moral authority in the Church that suggests certain parts of the body may never be touched. In fact, for many couples stimulation of the genitals during foreplay is necessary in order to prepare both the man and woman’s bodies for intercourse. The key question would seem to be is this being done as a part of the sex act, or is this being done as a substitution for the sex act?