No idea what you mean by "force of law."

As Lord Coke explained centuries ago, preambles are a “good mean to find out the meaning." 

Blackstone referred to preambles as intended to guide the interpretation of laws.

"We the People" cites the Founders contemporaneous views as to what the source of their claim to sovereignty was. Pretending that democracies and "constitutional republics" are at some fundamental contradiction is nonsense and tends toward playing at sophistry.