To those who don't know, most large companies already have a structured pay table. Try working at AT&T or McDonalds, and you can probably predict where your salary will be in the next 5-10 years. Real negotiation for most people in most positions mainly happens in small firms and startups.
Lack of salary negotiation will only scare away well qualified candidates who don't fit some arbitrarily made rubric (which will almost always back out to years worked, which is a terrible standard). Imagine if by paying 20k extra, you can get one of those mythical "10x rockstar" engineers. Would you remove your ability to hire him?
By opening up everyone's salaries, it will only hurt the startup culture, as it will only make people dislike each other. I often found engineers and business development people devalue each others work, in large part because neither party can understand the work of the other. Imagine them knowing each others salaries! Each side can find a justification on why they are being under-compensated while the other over-compensated. Startups need cohesiveness to survive.
Lastly negotiation is a valuable skill in the workplace. Interviews reward people who can handle stress and negotiate. Imagine a shipping date is imposed upon you, and not all the features can be included. You're going to want a leader on the engineering team to negotiate with the strategy makers to find an equitable solution. De-emphasizing negotiation is de-emphasizing a critical human skill.