Why should hardware be involved in security?

The logic was if the hardware is not functioning correctly, how can you rely on software running on the hardware to do so?

A lot of security is about process isolation and correct virtual memory implementations, you simply cannot do something like logical->physical address translations efficiently in software, it needs to be initiated by L1 cache look up (hence the cache's tags to eliminate false positive hits) and available for L2/L3/DRAM fetches.

Then again software being mutable is what hostiles rely on, you need the OS & hardware support to harden a system against expoitation, a program that's reentrant, relocatable or dynamically linkable simply cannot know what logical addresses it uses. Even so without hardware support where would the immutable correct address tables be stored, so errors cannot be exploited to patch the program?