Why did the colonist find the arguments and commonsense so persuasive

Because at that time, colonists were already so angered by everything that they had been subjected to by the British such as the Stamp Act, Coercive Act, Tea Act, no colonial representation in the Parliament, etc. Common Sense has encouraged colonists to act on that anger and frustration basically stating that it was ‘common sense’ to want to fight for their independence from Britain.

Assemblies do not have written codes of laws. laws are matters for magistrates and courts, not assemblies. codes of law are things such as civil law, criminal law, and constitutional law. what assemblies have are procedures regarding debating, voting and other business they might carry out.  also note that rome had three assemblies: the assembly of the soldiers, the assembly of the tribes, and the plebeian councils.