Meaning of Villainous dictum

[Cooliegirly]

"...no adventure too perilous for him to undertake if consistent with the character of a civilian who was at heart a soldier, and who in good faith and without too much qualification assented to at least a part of the frankly villainous dictum that all is fair in love and war."

What does the sentence mean? I looked up all the words I wasn't familiar with but still unable to understand the sentence.

[Mister Micawber]

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Roughly:

He was not afraid to try anything that a brave and noble person who believes that 'all's fair in love and war' would do.
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Native English teacher at Mister Micawber's

[Cooliegirly]

[Mister Micawber]

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"All is fair in love and war" is the villainous dictum.

Qualification = a statement that limits or restricts some claim. 'Assented unreservedly...to the dictum'.
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_________________
Native English teacher at Mister Micawber's