Catholics aren’t against all fertility treatments — only those that involve the destruction of embryos, obtaining genetic material through means that go against Catholic teaching, and/or “selective reduction”. The latter is a “polite” way of saying abortion. Many times, more than one embryo is implanted and many don’t survive or are culled if found to have abnormalities. I am not sure how anyone can call any of the practices above harmless or OK. The means do not justify the ends.
Even if no embryos are destroyed, IVF is intrinsically immoral because you have to commit a mortal sin to obtain the seed.
Doctors should be doing everything they can to help couples conceive naturally instead of sticking their pipettes in the middle.