"We never worried about "security" in the old days of processor design"
How old is old ? MMUs have been around a long time now.
"We never worried about "security" in the old days of processor design, we were far more worried about incorrect access causing a crash and that took priority - with the result that modern security issues were mostly nonexistent."
Seems to depend on where you worked - some vendors never embraced KISS. The protection features of the DEC Alpha were far easier to understand, use, test and verify than the equiv plumbing on the much older i386 for example.