It's a real stretch calling every browser an adware because of the default search engine deals they make. Since every browser already includes an option to do a "quick search" through a search field or the address field, and would already be including a list of search engines for this, users don't mind if a few sponsored search engines find their way in the list as long as the browser doesn't force them to use it or prevent them from modifying the list. The ability to search from the browser, and the list of actual search engines to do this provides a real benefit to the users. Bundling intrusive ads into the browser not only provides no tangible benefit to the user, it also harms them - there's the loss of privacy associated in the data collection of personal data to display these ads and the waste of a users time, bandwidth and computing resources to display them. (This is also why users find a list of sponsored bookmarks more irritating as it provides most no benefit).

The loss of trust and respect also needs to be considered - when you start doing data collection and introduce intrusive ads, how do I trust you to know the data collection stops?