Why do people think that privatization would make things like infrastructure and education​ worse?

The problem stems from monopolies. Take something like the power grid, it's too expensive and there's not enough space to build multiple sets of poles, transformers, and power plants, so whoever owns the existing ones would have a monopoly, and wouldn't be bound by market forces at all. They'd have little reason to improve their service, reduce their prices, or attend to their customers. That's why power is run by publicly owned coops, and/or highly regulated. Same with water.

Many railroads are privately owned I think. In fact, there's one between Orlando and Miami due to open this year. The reason a lot of track is publicly owned or at least subsidized though, is because railway profits dropped off dramatically after the automobile and airplane took most their passengers. Many rails were looking at going under, so in order to preserve the service and infrastructure, a public deal was reached.