Are Flea Collars Dangerous?

Well, I guess I'm aging myself if I tell you that while growing up... the cats in my family wore flea collars. What was the alternative back in the 80's??
I never liked the smell and I always knew when my mom put a fresh collar on the family cat Blackie. Blackie would have an awful smell for days. And she was obviously bothered by the collar of chemicals strapped around her neck to protect her. Hmmm...did it really help or is that what created her nervous twitch?
A generation afraid of the Plague's return??  Flea potions have come a long way since then. Now, monthly drops are used. Fragrant free and seem to do the job. A bit pricey but a small price to pay to protect yourself from the Black Death...right?
Let's face it...fleas are gross and every pet will bring them into your home. That is the reality of having a family pet that ventures outdoors. There is simply no escape from the little travelers. Should we fear the return of the Plague? Is that why we obsess over bugs and fleas? I think not.
So I ask a few questions; do these flea potions really work? Do these concoctions do more harm than good? Just something to think about..
This link suggests that the chemicals used on flea collars just might be harmful. You decide.
Here kitty kitty..Earth Talk: Flea-collar chemicals are dangerous