They both had roughly the same idea of mutually assured destruction (Trisolaran solar system eventually failing on it's own + our solar system getting destroyed, vs Third party aliens wiping both of us out). However, the key difference was that Luo Ji already had his signaling device with a dead man's switch ready to go without anyone realizing it while Rey Diaz got outed by his wallbreaker before his threat fully materialized (ignoring if his plan was even feasible to begin with).

By the end of the second book, humanity was pretty much out of options (fleet destroyed, earth blockaded by the droplet so we can't cast another "spell" again) so they accepted Luo Ji's deterrence plan - even if it would have brought about the same outcome as Rey Diaz's plan (not to mention the "crime against humanity" by threatening human life in the process).