It’s not that Youtube radicalize politics specifically. It radicalizes everything, and politics just gets swept along in the slurry of zomg.
In effect, YouTube has created a restaurant that serves us increasingly sugary, fatty foods, loading up our plates as soon as we are finished with the last meal. Over time, our tastes adjust, and we seek even more sugary, fatty foods, which the restaurant dutifully provides. When confronted about this by the health department and concerned citizens, the restaurant managers reply that they are merely serving us what we want.
Zeynep Tufekci highlights the problems with YouTube’s algorithm. There is a bias built in to support inflammatory content. In response to the post, Clive Thompson explains it this way: