I share your concern that this functionality could be abused, but disagree with your attempt to treat this as black-and-white or as a matter of personal character.

There are both ethical reasons and unethical reasons why an app-developer would want to know the other apps chosen by their users. On the up side, one could use the knowledge to prioritize improvements/integrations/compatibility with other apps. On the down side, one could punitively react to the presence of competing apps.

Assessing the ethics of how the functionality is used requires greater openness and transparency by everyone. Unfortunately, in a culture as closed as Apple's (eg http://www.pcmag.com/article2/0,2817,2375476,00.asp or https://developer.pidgin.im/wiki/WhyNoiOSVersion ), you are unlikely to see that kind of openness.