Scarecrow is about as successful as you can expect a pile of evil straw to be. His only ability, unless you count "highly flammable" as an ability, was having grenades that made people afraid of things. I'm sure he'd seem like a real asset to a carnival spook house, but when you're a terrorist organization made up of a gorilla and Solomon Grundy, fear is already on your side. No one's going to say, "Hi there, giant gorilla and Frankenstein! I see you brought 11 murderers with you OH MY GOD DON'T HORSEPLAY NEAR THE POOL! Please, I've got this thing about the water."
The Legion of Doom is run by a guy whose talent is a receding hairline, and he hires people whose powers are having a boat and tattling. Their abilities are moronic, but at least they're done with them in one step. Even if Scarecrow somehow gets the Super Friends to breathe in a bunch of his toxic gas, he's not done yet. He still has to find some of whatever he made them afraid of. Hitting Superman with a Fear of Spider bomb is really useless if you don't have a bucket or two of spiders on you.
You can't just rub a generic panic bomb with a ladder and tuna to turn it into a Fear of Heights and Fish grenade. It's all done with complicated chemical lab procedures. I'm only an amateur fear scientist, but I have to think that the formula for Fear of Heights and Fish is only a couple of drops of chemicals away from Fear of Bob Hope.
And if you take that as being true, which I'm assuming you do because you haven't had time to think about it, it would take months to figure out what each gas made you afraid of, and that's assuming you made a gas that causes fear of something that exists. It might be two or three years before you found out you made a Fear of Bigfoot grenade. And what good is all your trouble if you end up mixing a batch a gas that makes you afraid of something that everyone's already afraid of, like fat people in swimsuits or wolfman?
Scarecrow's main goal in life besides not being eaten by farm animals was to kill the Super Friends. But whenever he showed up, he went through an elaborate procedure that at best hoped to get them scared. He could have saved himself years and years of trouble if he'd have just thrown gas at them that killed them. There are four year olds mixing household chemicals who are accidentally deadlier super villains than Scarecrow.
Fear Fact: The human body only has so many chemicals it can use for being scared, so for every new fear you give someone, you give them courage somewhere else. For example, when you suddenly become afraid of fire, your body will compensate by making you less afraid of fire extinguishers. And Fear of Heights will actually make you magnificently brave in the face of midgets.
On to Part Two: Scarecrow's Personal Homepage!