How do you expect companies to understand how their products are used for improvement purposes without telemetry? Honest question.
Data analysis is difficult to perform and understand well. It is easy to draw mistaken conclusions or to twist results to show the conclusion a person wants, and using detailed numbers can lead to a false sense of confidence in the results.
Companies are first and foremost optimizing for their benefit, not the user. Detailed tracking can uncover interesting ways for a company to make more money at the expense of the user.
Telemetry doesn't make it possible, it makes it less expensive.
2) Conduct user studies
How are companies that aren't software vendors and aren't able to spy on their customers able to do it? Did software companies not have good ways to do this before spying on their users?
Only listening to data from 1 & 2 results in the sort of angry posts you frequently see on HN complaining that devs aren't listening to "real users" or have the wrong priorities.
You end up needing data from additional sources, telemetry being one of them.
If that's the sort of responses your studies produce, then your studies are seriously flawed.
Significant bugs can affect only 1% or 0.1% of a browser's userbase but at Chrome scale or even Firefox scale that's like a million people. If you don't have telemetry it is REALLY hard to hear from those people about their problems and understand them. There simply are not alternative solutions that work half as well as opt-in (or opt-out) telemetry. People who say web browsers don't need telemetry are simply ignorant of what it's like to ship one and try to keep it working in the face of a constantly shifting environment - broken drivers, broken VPNs, malicious websites, malicious extensions, broken hardware, and users who are confused or tired or simply just bad at using software. No one is speaking on their behalf, you have to dig their suffering out of the data by looking at crash reports and performance metrics.
Shipping a web browser used by a million (or a billion) users means that you have a responsibility to do a good job. If your browser is not well engineered and reliable and responsive to users' needs that can result in data breaches or third-party server outages when your browser misbehaves or incorrectly channels user intent.
I'm personally a fan of making usage telemetry opt-in instead of opt-out, but browsers are a case where I don't opt out because I know how important the data is for browser vendors to make informed decisions.
This is of course different from sending your browsing history to Google, Microsoft, or any other company. I encourage people not to opt in to that stuff and not to sync their history/bookmarks/etc to those companies.
It's probably no accident that spying on users got popular just as this became the case. Constant network traffic while web browsing didn't start to become the norm until late in the '00s, either. If you weren't clicking links, you could often open Wireshark or sniff with Netcat and see nothing. Not from your browser, not from anything. Certainly ~nobody was collecting heatmaps of where you move your mouse, or firing a network request if you selected text. Or recording entire user sessions for playback, or so you can watch them live (god, those tools are creepy as hell)
When the internet was young, and most people were using dial up connections, just collecting the dates and times that a person was online and using a program was (and still is) a massive violation of privacy. Software "phoning home", even just to check for updates (collecting IP addresses, timestamps, and version numbers) was enough to get your software branded as spyware.
No software company needs to know which hours I'm awake, when I'm using my computer, which hours I work, which hours I use their program, how long I use their program, how long it's been since I last used their program, etc. It's intrusive, entirely none of their business, and it's insane that they all feel entitled to that kind of information.
If I print something, don't print something, or what the things I print are is also none of their business. Neither is what I'm printing it for, where I put the printout after I take it from the printer tray, or if I use tape or a thumb tack to secure it in place, but you can bet that if software could easily collect that data it would and somehow it would be considered impossible to write good software without that information.
From a privacy standpoint telemetry is always invasive, which is why I disable it any way that I can. Even without the privacy aspect telemetry is a bad idea. I don't want program updates that remove features just because I (and others) don't use them very often. I don't want updates that constantly shuffle the UI around according to how they think "most" people have been using it this week. I don't want my workflow disrupted every few months because it's uncommon. I don't want the way I choose to use the software on my device to influence how other people are expected to use it either.
Telemetry is much better when it's limited to reporting errors and bugs, but even that should be opt-in only.
If a team is so unfamiliar with their product and customer base that it cannot take action without telemetry, maybe they're not the right team to make that product. Statistics are not a substitute for domain knowledge.
I feel like people who are fully against telemetry never had to deal with such issues in big apps