It's true - charging for something that was once free can be risky, but it isn't always bad as some might believe. I have great respect for businesses that charge for a service that provides real value - even if it was once free. Often times (especially in the startup world), companies start out offering a free product (operating at a loss) to gain market share. It's not often the best strategy, but in some markets it's one of the few ways to break in and gain traction. Obviously, you can't sustain operating a business that way forever, so you eventually have to make up for it somehow.

Unfortunately, a lot of tech companies have (perhaps unintentionally) conditioned consumers to expect software to be free. The terrible consequence is that in response to that pressure, many companies choose ethically-questionable ways to make money when they need to, rather than simply charging a fair and honest price for their product (this includes selling users' data, overwhelming the user experience with ads, in-app purchase shenanigans, etc). Paying fair prices for things we use isn't the most appealing idea in the world, but (in my opinion) we probably need more of it, not less.