Question

Why was signing the Declaration of Independence a decision that,if things turned out wrong, could be fatal?

Answer 1

I believe all the signers would be executed by the king of Great Britain and the colonies would fall back under British rule.

Answer 2

The Declaration of Independence was pretty much treason, which is punishable by death. So by signing their names they were basically openly saying they had committed treason on a letter drafted to the king (which is why John Hancock wrote is name so big- it was basically a "s/crew you, come and get me" to the king).