Why do Christians equate other religion's deities with "Satan"?

Seriously, most Christians will claim that every other religion and its deities are really the works of Satan and that the Christian god is the only true one. I'm sure this is news to all of the Muslims and Hindus who had no idea that they were actually worshipping an entity that is the personification of pure evil until informed of this by Christians. Funny considering that the Judeo-Christian god is either directly (the Bible) or indirectly (historical fact) responsible for more deaths than most of the other religion's deities combined (with the possible exception of Allah). Christians, if someone else worships a different fictional Supreme Being than you do, why does that automatically make their fictional deity the embodiment of pure evil? Is a little tolerance too much to ask?