There is a duplicity in Drifloon's appearance that I firmly believe is core to its being. Drifloon must look inviting and fun to lure children to grab hold of it so it can drag them to the afterlife. If you look at certain details, you will see that Drifloon is anything but.
First, let's look at the facade. Drifloon is a purple balloon with a cute face and cute white swirly hair. It has two strings dangling from it with yellow hearts at the end of each one. It looks harmless. It looks fun.
But wait. The cute white swirly hair is what I'm sure is meant to be a cloud. The back of Drifloon's hair is gray, not white. This cloud is stormy.
The hearts at the ends of its strings are turned upside down. When a symbol is turned upside down, it often means the opposite of what the symbol signifies right side up. A cross, for example, represents Christianity, while an inverted cross symbolizes atheism. Hearts symbolize love, and so an inverted one can absolutely be seen as hate.
There's also an X on Drifloon's face. This is likely the most obvious sign of Drifloon's duplicity. X's are extremely negative. Think back to school. No one likes seeing X's on their papers, because it means you answered a question wrong. Drifloon is X'ed out. Something about Drifloon is definitely not right.
Drifloon's stormy hair, the inverted hearts, and the X on its face are clear marks that Drifloon should be avoided.
Drifblim, clearly meant to resemble a hot air balloon, retains some of Drifloon's same warning symbols: Drifblim kept the stormy hair and the X on its face. The inverted hearts are gone, but replacing them are red eyes. Red eyes are a sign of evil in many video games, TV shows, and movies. If you want to make a villainous character stand out from the protagonists as evil, give him red eyes.
The warning signs are all there on Drifloon and Drifblim, but people keep gravitating to them in the Pokemon world. People and Pokemon even use Drifblim as transportation. They are just asking to go missing.