Ugh, As any female may know, have you ever accidentally sprayed hair spray in your eyes? Burnns for a bit. Hairspray is legal. Pepper spray may not be, and you could get into trouble in a foreign country. Or, the pepper spray can be taken from you by someone stronger and used against you.
Mark, you should be okay. I realize bad things happen to good people. But, practice common sense, don't be lax but don't walk like you're ready to combat. Of course, don't hang your bag on a chair, hook or place it on a table. That's the 'beauty' of a cross body bag - if it's a decent size, you can keep it on you at all times - even enjoying that glass of wine at an outdoor cafe :)
As a woman who traveled to Rome twice, I often walked by myself here and there - at night. I really did not feel unsafe. I totally understand your travel is to Paris. Rome gets a bad rap too. As a little comparison, that's why I referred to it. I've not been to Paris, but, it's another large city that attracts thousands.
When a train or bus approaches, and you feel it's too crowded, then just wait for another. Don't overthink some stuff, cause then that's when you "may make a mistake."
It's probably not necessary for a whistle. But, if you feel better taking one - then do so. Clip it to a key leash if there is one in your bag.
Actually, I got a little LED flashlight that I clipped to my bag's inside key leash. It was a $1 at Walmart in the camping section. The light is really great and not flimsy. It's a plastic, but sturdy casing - not heavy. I found that to be useful in Rome later at night when I was unsure of curbs, walkways or protruding cobblestone.
I understand the term you used to describe a group of people may have been common in the past, but, it's best to not identify any one person or group. Certain terminology can set off a person making them more angry and harmful to you.
Thieves come in all. Just don't make it easy for a pickpocket. Have a good trip!