The biggest issue I see is people becoming more lazy and accepting all information without questioning the source and their intentions. Its already bad now but I can see it getting worse.
Critical thinking in general is severely lacking in today's society.
with or without social media, people are generally dumb as fukk. that'd why america sells the whole "anyone can make it" idea, knowing that 90% of people are their own biggest obstacle to that. i was watching a documentary this weekend and it showed one of the tea party town halls, dude was up there stating what the "black liberation movement" is (basically socialists who want to kill white people) as well as tons of other misinformation, and the 100 or so people there held to every word, one woman said "i knew things were bad, not this bad, it's so nice to have a teacher who informs us"...
as they all walked out with this dude's book.
but this is what happens when you have corporate controlled, politically biased, opinion based media, there's no trust and no fact checking, everything goes, not sure why we're calling out the issue on social media when it's top down. if there were ever a time we needed well informed, sane, independent media that factually reports the news, including BALANCED analysis (conservative and liberal - not necessarily republican/democrat) it's now. i wish i had the passion for media, i'd really try to start this.
We lawst. 
