For starters, default to not install the crapware.
Alternatively, instead of creating more required user actions than necessary. While the software is installing, show splash screen type adverts of software the user may also be interested in installing with a way to add them to the install queue on the fly or select it after the install is done.
Sure, they rate of install will be shit, but if they were really interested in doing the right thing this wouldn't be a problem and the users of said applications would be legitimate users, not just angry computer illiterate people.
That's just it -- they aren't.
The sole purpose is to generate revenue. They don't make money when users don't install the software.
So the population IM attracts are precisely those unscrupulous developers and programs that profit from questionable behavior. Working in a proper manner runs counter to their customers' goals.
The examples are usually just advertising other products they own, or features within their software so not exactly direct examples but its not a huge jump by any means.
While I agree the population of customers they will attract are those shady toolbar guys, it certainly doesn't follow that they cannot make a business out of pushing good software. I think as long as they tailor the ads to relating software or software people will likely install alongside the current piece it could work. Taking the high road could even payout bigtime down the line when more developers catch on and realise it won't detract from their image/brand by using such a service.