Step 1: Read the description carefully.
The clue is: a person who deliberately sets fire to buildings or property. The key idea is a strong urge to start fires on purpose.
Step 2: Look at the word root.
The prefix pyro- means fire, and -maniac means a person with a strong obsession. Putting these together points to someone obsessed with fire.
Step 3: Check option Iconoclast.
An iconoclast attacks long-held beliefs or traditions. This has nothing to do with fire, so it is wrong.
Step 4: Check option Misanthrope.
A misanthrope is a person who dislikes other people and society. This does not match fire-setting, so it is wrong.
Step 5: Check option Philanthropist.
A philanthropist helps others and gives to good causes. This is a positive, helpful word and the opposite of destructive, so it is wrong.
Step 6: Pick the matching word.
Pyromaniac means a person obsessed with fire who deliberately starts fires. This fits the clue exactly. \[ \boxed{\text{Pyromaniac}} \]