The most common and most likely answer to this crossword clue is the 14 letter word LIBERTARIANISM
I've seen this crossword clue in The Sunday Telegraph
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Buddy explains!
The straight part
We know that "Laissez-faire doctrine" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case laissez-faire doctrine = libertarianism.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
LIBERTARIANISM noun- A political philosophy maintaining that all persons are the absolute owners of their own lives, and should be free to do whatever they wish with their persons or property, provided they allow others that same liberty.
- The doctrine of free will, as opposed to necessitarianism.