People liking thigns can be infectious, this is the core power of "hype culture". If what your saying is that people hating things can also be infectious, than this is true, but to a much lesser extent and usually only affecting nihilistic people with deep-seated self image issues. I'll grant you that these people have grown in number lately and control a large mindshare within western media, but one is a coordinated effort to police how people think and feel, and another is people liking stuff and enjoying when other people also recognize and like the same qualities they do in that thing...it builds kindship and community.
It would be two sides of the same coin if the motive was the same, but they couldn't be further apart, if you enjoy say; the new spiderman movie, and someone else doesn't enjoy it, you won't nessarily dislike that person for having a different opinion, you'd simply choose something else to talk about. But if you are pro-LGBT and someone is a homophobe, you'd probably not want to associate with that person, and if you were militant in your beliefs you'd probably try and make sure nobody else associates with him either (cancelling him).