I think people are upset about this not just because extra software is being requested to be installed during the desired installation (it's not just an ad, it's an embedded installer), and not just because SF is trading in on their past reputation, but also because of the type of software that is being installed. Malware is too strong a term for it, it's possibly adware, but definitely junkware. It's software that purports to "make your system run faster" and the methods it goes about to accomplish this may actually make it run slower (clearing the system cache) or even cause corruption (clearing the system cache incorrectly). The software may actually cause problems on your computer while making unsubstantiated claims of helping it.
To be clear, I personally wouldn't mind advertising and installing software from an installer if some minimum criteria were met:
1. The software being advertised was actually checked by someone to confirm it had some use, and was not in fact detrimental to the users.
2. The accept/install button was not put in place of the button that moves the install process along normally.
3. A separate installer window was launched to make it obvious what was happening. No quiet background installs allowed.
I should clarify that I was only referring to this screenshot - https://i.imgur.com/hNDdz4P.png - the other one is worse but I didn't notice ggp had an album of two (unless they changed it.) without the picture it would be a lot worse.