There's a father in the UK who would disagree with you. His daughter, who was very quiet, introspective and not very religious was introduced to ISIS via Twitter. They carefully groom, have "handlers," who spot the girls and then hand them off. They're then fed a steady stream, similar to what you see on your Twitter and Facebook. With the aim to gradually move you from center and an "entertaining extreme ideas," without any aim to do them yourself. Then one day, "Come check it out for yourself. Here's Twitter accounts of others who are here and having a great time!!" The UK girl hid her trip from her parents who had 0 idea until the police showed up. The sick irony is the police had previously contacted the school, who sent home a letter with the girl for her parents to read. Guess whether parents saw it? Long story still long... It is good that Anon is shutting these down.
For the people asking why intel communities aren't shutting them down: They're intel sources. Why would you shut down accounts when they tell you TTPs, SOPs, areas of influence, capabilities, locations (eg. idiot Twitters a pic of the ISIS HQ, which is then bombed within 24 hours), etc. Besides, no manning for this as there's no DoD or IC requirements to "shut down propaganda accounts."