Didn't even realize the extent of the referral codes. Imagine if Chrome auto-inserted their own amazon affiliate links when people typed in Amazon.com - people would be up in arms.
It's traffic attribution; Brave showed the affiliate option to users via a pre-search UI panel in the browser (screenshot: https://brave.com/wp-content/uploads/2020/06/image3.png). Users could then decide to use the top suggested result, or not. The mistake here was matching on fully-qualified URLs, as opposed to search-input exclusively (the intended behavior). You can read more about it here: https://brave.com/referral-codes-in-suggested-sites/. No element of this is malicious.
As for what others do, traffic attribution is common. Open Firefox and perform a search from the address bar. Long before you press Enter, Firefox has already sent keystrokes off to Google.com (assuming you haven't changed your default search engine), along with a tag on the URL identifying Firefox as the source of the traffic.
The problem is that referral programs are intended to get people who wouldn't have signed up for a site to use it, and for binance that means getting people not already signed up to sign up and trade crypto on binance.us. This includes the referer getting up to 40% of trading fees[0]. Even for the example where a user chooses between the search 'binance' and `binance.us/?ref=`, in both cases they were already planning to visit and/or sign up for the crypto trading site, Brave didn't do any referring themselves. The profit sharing aspect makes it far-removed from the notion of just being for traffic attribution.
If you read the post covering the feature in Brave, and reviewed the screenshots of its implementation, you'd see that the intent here was to respond to user input, and offer the user the option of using Brave's referral link. The intent was never to coerce users into using the link; it was merely presented as an option—a clean and clear way to support Brave development.
It is still an example of traffic attribution, as is the case with Firefox sending your keystrokes to Google asynchronously (marked with the Firefox identifier). This is how Firefox continues to get paid, by sending users over to the Google search engine. In the case of Brave, this identifier was shown to the user prior to any network activity. That isn't the case with Firefox (and nearly every other popular browser).
If binance is fine with it then sure, but it's not like Binance is getting any extra sign-ups thanks to Brave from these suggestions, they're just giving up a percentage of their trading fees when it happens (the user would have signed up regardless of if you allowed them to use the optional referral code or not).
Why would people be in arms? Seems like a perfectly fine thing to do. They are literally referring people with buy intent to amazon's deep product pages.
I've since clarified my comment, I meant if Chrome inserted affiliate links, not Google (search).
For chrome doing it, the same applies to Brave as those people would have visited binance.us regardless of if Brave inserted their referral code link there.
