I disagree: increased letter spacing is a form of emphasis.
Perhaps you are confusing it with kerning, which does make text easier to read, and which absolutely should at all times be automated (no exceptions, not even for 'display' text).
Also, I quoted "designers" in the strict sense of scare quotes: to indicate that the word's meaning was different from (my understanding of) its usual definition. Most people who design things are not visual artists; properly construed, "designer" is almost synonymous with the modern meaning of "engineer". However, on the web at least, its meaning has been blurred.
You are free to disagree, you're still wrong. Kerning and tracking are about the space between two letters, adjusted dependent on the form of the letters in question to reduce the appearance of gaps between same.
Letter-spacing is the overall spacing between letters and is again purely visual, used to prevent unsightly gaps toward the end of the line in justified text or to make uppercase titles easier to read.
The only meaning you might possibly want to convey to an unsighted user regarding letter-spacing is a propensity for sheep rustling (however blackletter isn't a popular style on the web).
Non-emphatic letter-spacing changes are susceptible to automation, thus should be automated.
If, for instance, uppercase text requires wider spacing, the browser — or better still, the font renderer — should work that out; the designer should not have to explicitly tell it things like that.
Since, in any case, most manual typography is already algorithmic (if such-and-such condition, the spacing needs to be increased), and since the 'judgement calls' about the aesthetics of type are already encoded into the font by the foundry, manual typography outside the foundry is /obsolete/: machines can do it better, because they can use optimisation algorithms to find the best trade-offs (compare, for instance, TeX's line-breaking algorithm to the common manual approach of "first-fit, but backtrack if the solution is too poor").
Perhaps you are confusing it with kerning, which does make text easier to read, and which absolutely should at all times be automated (no exceptions, not even for 'display' text).
Also, I quoted "designers" in the strict sense of scare quotes: to indicate that the word's meaning was different from (my understanding of) its usual definition. Most people who design things are not visual artists; properly construed, "designer" is almost synonymous with the modern meaning of "engineer". However, on the web at least, its meaning has been blurred.