Why do you think non-profits should pay lower salaries than for-profits? It's good for the world if non-profits can compete with corporations as they tend to act more ethically. Also, from a macro-economic point of view, wages are one of the best things a company can spend it's money on.
As an aside, there are some non-profits that are well funded but don't pay market rate for their talent, and I sadly see them falling behind.
If you want a non-profit that you donate to succeed, you should hope that they're attracting and retaining the skilled talent needed to achieve their goals efficiently.
If salaries are unlimited, there's no more motivation to act ethically than a for-profit concern has. Instead of taking the fruits of bad behavior as profits, you're just taking them as salaries. Upper management just takes the place of stockholders/investors.
Non-profits commonly warp to the point that they're spending virtually no money on their stated mission.
edit: It might be even worse if all salaries fall within a narrow range and all of the workers feel as if they are sharing in the success of the company: the economic motivation in that case would be to become a monoculture of revenue-maximizing behavior, where employees with opinions that threaten cashflow would quickly end up isolated and/or expelled. If everyone gets a salary bump after implementing a dark pattern, there will be a lot of people rationalizing the decision.
