Contagion absolutely works for viruses and bacteria, but it isn't as simple as sit next to someone with a cold, get a cold.

It is more sit next to someone with a cold and your chance of getting a cold go up by X%. X is an impossible to quantify number because it depends on so many variables. When during the cycle of the cold did this happen? Are you a mouth breather? Are they? How well and when did the two of you wash your hands? Facing towards each other or away? Inside or outside? Sunny? What is your current short term and long term stress level? How is your nutrition status? Has your immune system seen that exact cold before? A similar one? How recently? On and on.

I sincerely doubt that anyone who ever had a kid in daycare believes that contagion isn't how viruses and bacteria spread. You'd be denying the evidence of your own immediate experience.

Since I had leaky gut, a massive standing stress load, while my last one was in daycare I caught the things they brought home about 2x as often as my wife who didn't have that chronic stress issue. It wasn't a guarantee, but it made my chances worse. For me X was always higher during every exposure during that time.