Ancient Rome had brilliant leaders but among the line were insane, degenerates. How is that possible?!?

Question

I will be studying about ancient Rome (modern Italy) and it's civilizations, cultures, customs etc. but about their leaders, of one, Caligula. During his 3 year(?) idle(?) decadent (?) reign why did citizens accept this and why didn't outside forces take advantage of this if they knew such weak persons were on the throne? Caligula doesn't seem to be a 'normal' person to be a leader possibly due to his tragic upbringing which might account for his mental strangeness which seems to continue towards insanity.

Answer 1

i'm italian and i studied at school the history of ancient romans for many years

the leaders were insane, degenerates mainly because they were intoxicated from copper, used to produce cutlery and plates, where they ate
and the copper is a chemical element that cause problems to mental health

Answer 2

You have to look at it from their times. They probably had a lot of spin. Also anyone that challenged the imperial family usually ended up breathing dirt. See the PBS series I Claudius.

Answer 3

during this period in rome's history the leaders were selected by heredity, not on each one's merits. every family tree has nuts.