I look at the slobs I work with and tell them a little exercise wouldn't hurt them every once in a while. A fellow co-worker is ten years my junior and a CrossFit fanatic and looks at me like I'm from mars when he sees me pull up on my bike in the rain. What the heck happened to Americans that RAIN keeps them indoors? I admit cold windy rain gives me a headache when riding in it unprotected. Also admit it's annoying cleaning dead worms off my bike. But I regularly clean and lube my bike so rain shmain. My BIGGEST concern is how visible I am to motorists in the rain. I will switch routes to stay away from cars that are driving with their wipers on. ( and defroster, radio, cell phone...)
Personally, I find it invigorating.
I will step off my soap box now, good post OP.