The most common and most likely answer to this crossword clue is the 7 letter word PIRATES
I've seen this crossword clue in The Daily Telegraph
P
I
R
A
T
E
S
More clues leading to the result PIRATES
- Very good values felons found in craft?
- Very good levels of pay for buccaneers
- A priest converted wrongdoers in the main
- Draws breath, since fleeing raiders
- Bad sailors getting good pay
- Destroyers at sea changing sides in course of exercises
- Goody-goody scolds baddies
- More than one brigand shown to be soft ‘hearties’ after he’s downed rum
- Good prices for freebooters
- Very good prices for those from Penzance?
Buddy explains!

The straight part
We know that "they’re dangerous in the main" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they’re dangerous in the main = pirates.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.
What does PIRATES mean?
PIRATES noun- A criminal who plunders at sea; commonly attacking merchant vessels, though often pillaging port towns.
- An armed ship or vessel that sails for the purpose of plundering other vessels.
- One who breaks intellectual property laws by reproducing protected works without permission
- A bird which practises kleptoparasitism.
- A kind of marble in children's games.
- To appropriate by piracy, plunder at sea.
- (intellectual property) To create and/or sell an unauthorized copy of
- (intellectual property) To knowingly obtain an unauthorized copy of
- To engage in piracy.