A lot of ills are laid at social media's door, but I think this is a warranted one. Journalists were/are the beating heart of Twitter's userbase, giving it outsize influence through years of a minuscule userbase (eg there was a non-trivial period where there were more active in-stream users of Google+ than Twitter).

There have always been media personalities, but Twitter has made that the default mode of the industry, and removed editorial safeguards from a dramatic amount of the journalistic conversation.

Less interestingly but probably more saliently, the economics destruction that the internet wrought on journalism has just destroyed the economic buffer that allowed them to build a culture of standards and principles (such as it was). People have always liked being affirmed over being informed, and the journalism market now forces journalists to deliver that.