I'm going to assume that's 100 degrees fahrenheit, right?
That's around 37 degrees celcius for us non-US people =).
I'm from Sydney, and we often have low 40's (Celcius) during summer. We currently have raging bushfires over here in some areas =(, and it's easily 40 degrees.
I bike to work (and also for fun on weekends) during that sort of temperatures, and I've never been worse for wear...
I also jog regularly during that weather (although I find that harder than biking - less breeze).
Mate - you're not going to get heat stroke from riding your bike a few Km at 37 degrees, seriously...
As your fitness improves, you'll probably find it easier.
Just stay hydrated (you do carry water, right?), apply sunscreen, and you'll be fine. Sure, it's harder work than driving a car, but exercise is hard work (despite what those late-night TV ads tell you).
Yes, you are right. I live in Houston and I bike for 12 miles round trip almost through out the year except when it is cold and windy. And if you are commuting for work, you are not going to face the peak heat in the middle of the day during summer. But the roads are not completely bike friendly in here and there is problem of stray dogs.
I'm not exactly disagreeing with you, but humidity makes a HUGE difference. I've been in 100+ degree heat with low humidity (115, actually (46.11 C)) and it's downright pleasant. I've also been in 100+ degree heat with high humidity and it's almost unbearable. The difference is, in low humidity your body does a fantastic job of cooling yourself, while high humidity prevents your body from dissipating as much heat since your sweat doesn't evaporate. I'm not saying you're wrong, but temperature does not describe the entirety of a climate, nor its safety.