Using app mamager and many other apps listed here requires root privileges. This means that you are able to modify almost everyrhing on the phone. From one side you are basically free to do what you want, on the other is true that becomes easier to escalate privileges. It is also true that if someone targets you and wants to hack your phone, he is gonma do that in any case because there are a lot of other security holes anyway. If you are using a GNU/Linux operating system, you have to deal daily with root privileges and this is not considered a problem. On phones its problematic to let users play with them because many of them will brick their phones like nothing so, it was chosen to limit the power that the user can have but this is an injudtice for who wants to do something more technical. In my opinion, the pros of having root privileges unlocked surpasses the cons. Especially if you mitigate the risks by doing regular backups and not putting all your life in your phone.