First, let's deal with your basic question, the difference between "debe" and "debería".
I want to start with a simpler pair of sentences than yours.
Él cree que debe orar.
Él cree que debería orar.
Both of these can be translated by
He believes he should pray.
So what's the distinction in Spanish? The first sentence carries the ...
They are almost the same. This is supported by the DLE:
2. loc. conjunt. Porque, puesto que. Ya que lo sabes, dímelo.
and by Fundéu:
Porque, ya que o debido a que son algunas de las alternativas que se recomiendan en lugar de la expresión y es que con valor causal.
The very slight difference is that ya que gives the hint that the cause is a ...
Cretino and idiota are analogous to their English cognates "cretin" and "idiot" - words which originated as medical terms for people with various cognitive disabilities, which by extension gained pejorative senses as general insults attacking a person's intelligence.
As derogatory senses are acquired, new technical terms are coined to ...