I'm also not an epidemiologist, but I can think of at least one disease where the advice "catch it when you're young and you'll have stronger immunity" has a serious downside: chickenpox. A subsequent case of chickenpox itself is rare, but the herpes zoster virus remains dormant in the body and can re-appear as shingles in adulthood. I don't know the probability of that vs catching chickenpox following vaccination.