From my experience, people against open source often have buyers remorse. They often paid egregious sums of money for proprietary software that, to be fair, works well and includes enterprise support. When the same someone encounters the same solution but free and open source, they start rationalizing. The difference is mainly marketing, where open source projects have little to no marketing budget and are largely denied by market makers. Proprietary solutions can afford the seminars, thousands of dollars a week on ads, and other perks which increase discovery.

The moral of the story is to be careful listening to people actively tarnishing open source as they are a crowd of bitter people. A tell-tale sign is that they don't talk about the benefits of proprietary technologies such as the level of customer support and technical expertise that comes with the bill and instead only bash on open source.