In addition to wutbrodo, I find that Wikipedia is actually a great starting point to find out more information for yourself.
For example, take the comment that you originally replied to, which asserted "Susan Rosenberg literally bombed the Capitol in 1983 and now serves as vice chair of the board of directors of Thousand Currents, a "non-profit foundation that sponsors the fundraising and does administrative work for the Black Lives Matter global network, among other clients.""
That is obviously a great soundbite that seems tailor made for the "the left ignores the terrorism on their side" argument. But on the Wikipedia page for Susan Rosenberg, you can see what her level of involvement was, see how she was punished (she served 16 years), see what she's been doing since she was released from prison, and follow lots of links to original sources, like the tax return for Thousand Currents.
Snopes is also a great source for stuff like this: https://www.snopes.com/fact-check/blm-terrorist-rosenberg/. Again, you don't have to agree with the simple "true/false/mixture" checkbox Snopes puts on their stories. Just read the article, which always has tons of well-researched factual info, and make up your mind for yourself.
My main point is that whenever you see some soundbite or statistic on Twitter, Facebook or HN, it was often taken out of context in order to make an argument. It's usually pretty easy to use Wikipedia as a starting point to find out more about that context.
And to be clear, while I obviously have a point of view, my main point is that you shouldn't take anyone's opinions at face value - the Internet actually makes it pretty easy to find original sources.