Non-conventional thinking here, feel free to tell me why this is wrong/stupid/dangerous.

I am young and healthy, and when I catch a cold, I think " cool, when I recover immune system +1." I take this one step further though, when I don't get sick for a long time, I start to hope I get sick because I want to exercise my immune system. I know this might sound obviously wrong but can we just discuss why exactly?

My priors tell me that actively avoiding any germs and people to prevent getting sick is unhealthy. So I have lived my life not avoiding germs but also not asking people to cough on me either. But is there room to optimize? I caught something pretty nasty that lasted a month, and I am sure I got it from being at a large music festival breathing hot breathy air, but better now than catching that strain of what ever it was, when I am 70 right? And I don't mean I want to catch a serious case of pneumonia and potentially die, I mean what if there was a way to catch a strain of the common cold every now and then deliberately.