I wouldn't compare tumblr to the libraries of old. At least in libraries you could expect those inside it to have an obligation to academic pursuits and values. Social media, on the other hand... I know of several people who get their news off of tumblr. I also know of several other people who have become Internet feminists. I think the Internet's made it easier to homogenize what we pay attention to - saturate our communications with information and opinions that agree with our own. To give another example, it's just as easy to like and share something as it is to close the tab or dislike it - a click, essentially. Given people being people, I'd imagine their Internet use to tend towards things they like. While it comes down to the individual, people are still people. Perhaps this is a cynical assumption, but I imagine most people end up closing their minds instead of opening them.
I agree, most people will. But I don't think you can exactly blame them. Society trains us from the day we are born as to what is "good" and what is "bad." If you don't approach it with a bit of an impartial attitude--ready to learn--from the beginning, then you most likely aren't going to get much out of it. If you go onto the Internet thinking that what you said about a controversial topic is true, and you Google something, or get some news from a Tumblr page you follow that also supports that same belief, of course it's going to only reinforce said opinions. And, while I agree that is how people use the Internet, that is because that is how they were taught to use the Internet. Not so much in a traditional sense, but taking examples and behaving in a way fulfilling the status quo. While the Internet is a tool, it is also a social outlet for a huge percentage of those who use it. Whether it be Facebook, Youtube, or even a website like PC. Due to that, we are still exposed to the pressure to conform or fit in, and honestly, despite what anyone says, I would say that most people feel that tendency at least a small amount. That narrows your mind. I mean, if were pro life, why would you be following a bunch of pro choice Tumblr pages? You wouldn't. Unless you were already an open-minded person to begin with. So if you, like you said, got all your news from Tumblr, you would only be exposed to the news from a probably heavily biased source. If you tried to speak out against anything this biased source posted, you'd get nothing but hate and probably a few death threats or something.
But, if you wipe the social aspect out of it, it alleviates some of the pressure to automatically believe the popular opinion and be liked by people. Honestly though, if you do that, is entirely up to you. The same could occur in a library. The Internet could provide mistruths, but I bet you a lot of published authors do too. It honestly depends on your mindset. You could search for unbiased information, you could cross-reference information from the two different sides, or you could take all your information from one side. On the internet, or at the library, it doesn't matter. What I think makes the internet so exception is that it has so much information so readily available. While a library has a great amount, unless you actually live by a HUGE one, you might not actually have much going for you in the library. I know my local library is terrible, tbh, I think it only has a handful of books from this decade. When I went to high school, the newest books the library had were from like 2005 with the exception of like the encyclopedias or when the book fair came around. The internet has access to so much more information, and as long as you approach it with an open mind as you would tangible information, then you should be fine.