I love the cute vibe, but I feel the need to rant:
“strengthens the immune system” doesn’t mean much. And if you take it at face value, it’s probably a bad thing, atleast in the West, more people suffer from overactive immune systems (allergies, autoimmune diseases) than underactive ones.
I do remember a friend's mom. She had a lot of allergies and was big into woo-woo. Anyway, she once told me that she was doing something with her essential oils and orange juice "to boost her immune system and deal with her allergies."
while i get your complaint's point, i think you're a bit over-simplyfying this.
the immune system isn't just "weak" or "strong". it must be calibrated.
for example, allergies exist because the immune system focuses on the wrong things. A strong immune system can be considered healthy and a good thing; that doesn't mean it should indiscriminately kill anything it encounters. So, the story is a bit more complicated.
for example, it's considered healthy for children to play in the dirt, because it teaches the immune system what to focus on.