Sardonicus here explains why he left Facebook. Briefly, he left it because it had become for him an impediment to spiritual growth. I concur and generalize: inordinate consumption of any and all mass communications media militates against spiritual health for all of us. Mass media content is a bit like whisky: a little, from time to time, will not hurt you, and my even do some good; but more is not better!
But why, exactly? Here is one answer. The attainment of mental quiet is a very high and choice-worthy goal of human striving. Anything that scatters or dis-tracts (literally: pulls apart) the mind makes it impossible to attain mental quiet as well as such lower attainments as ordinary concentration. Now the mass media have the tendency to scatter and distract. Therefore, if you value the attainment of mental quiet and such cognate states as tranquillitas animi, ataraxia, peace of mind, samadhi, concentration, 'personal presence,' etc., then you are well-advised to limit consumption of media dreck and cultivate the disciplines that lead to these states.
Of course, the quick answer I just gave presupposes a metaphysics, a philosophical anthopology and a soteriology that cannot be laid out briefly. So here are some links to related posts that fill in some of the details.