Online journalism has become more accessible to the casual class of society due to a growing number of internet users and social bloggers More content can be easily accessed and proliferated using the online medium but at the same time with such a large amount of content out there, it is hard for the casual subscriber / reader to delineate truth from fictionand cross reference anything that may seem as more of an opinion than actual record of an event (unbiased). 

Mainstream journalism has built up a larger organization and therefore has more stability in the market. Also, they have the motivation through competition to get the news faster and with integrity and with a larger source of professionals working under the mainstream branches of journalism. 

Readers and viewers have a better chance of cross referencing stories and truly comparing the stories for facts. But at the same time the mainstream journalism empire has the monopoly power. Therefore, they can usually control the content that is actually coverered and thus limit their audiences from the world.