I think it is a confluence of factors, but primarily it has become much more visible due to the rise of social media. And by that I specifically mean that social media enabled far more people to actively contribute and communicate online to wider audiences than previously. Most of the people communicating undesirable ideas have not formed them recently. They have held them and repeated them very often, they simply haven't been accessible to others, searchable, indexable, etc. All of the various notions about requiring platforms to regulate speech online and similar will, at most, return us to that situation. That would not necessarily be a positive step. As an example, two sisters from the Westboro Baptist Church have left the organization expressly as the result of one of the sisters having her mostly deeply held beliefs questioned, challenged, and refuted on Twitter. Were that communication not able to flow, that group would still have two more members protesting funerals, spewing irrational hatred, and promoting a harmful ideology.

Human beings have a natural tendency to wish to categorize things in a binary manner, and they deal exceptionally poorly with situations that feature an abundance of both good and bad. They feel compelled, really compelled, to decide to pay attention to only one of the two possibilities and to minimize the other so that the opinion of the matter can be held onto more tightly. I personally think this is a tendency of deep biological origin (down to the actual functioning of the brain level) and it is something we must guard ourselves from buying into.

Another large factor is simply number and breadth of people communicating online. Children, adolescents, and young adults are very active online now. They are learning social skills and as our society totally and utterly abandons them in this regard outside of the Internet, it is the only location in the world where they can even have the possibility of interacting with other people as equals. Beyond the bounds of the Internet, they are treated and spoken of very poorly by all segments of society, and they bring their bitterness over that with them online. Human society has problems, and our desire to hide those problems should be resisted in preference to wishing to see those problems solved. Talking about it, and attempting to find successful means of solving those problems without compulsion but with education should be an actively pursued goal, IMO.