Etrecheck's only "malware-like" behavior is notifications, which can be turned off in the system preferences.
Its primary function is to identify hardware and software the machine has installed, and running in memory resident areas.
That's all it does.
Avast, Malwarebytes are able to identify and quarantine files known to belong to Malware and viruses.
In the early days Avast did have false positives.
But it has since become really effective as long as you turn off its notifications, and even comes with its own uninstaller, which is rare.
AppDelete 4.3.3 is a great utility to remove programs, but it isn't perfect, and you can use Etrecheck to identify programs that haven't fully disappeared after restart.
Devon Technologies EasyFind is able to locate all files on a system, including hidden files, and in safe mode delete any file as long as you have administrative access. And it doesn't need indexing like Spotlight.
Many utilities profess to optimize the system by cleaning system caches, update prebinding, repair permissions, and cleaning logfiles. In the early days of Mac OS X when it shared its space with Classic systems which didn't recognize its permissions, permissions repair was important. Apple's system caches though are constantly being written and rewritten, and if caught in the middle of being written can lead to an infinite loop of corrupted cache files. This in turn slows down your system. System updates do their own prebinding. Logfiles are cleaned up automatically as long as you leave your machine on overnight at least once a month.
