The phrase "most wellmeant" refers to something that is intended with good intentions, sincerity or kindness. Antonyms for this phrase would include words that suggest ill intent or negativity, such as malicious, malevolent, wicked or harmful. Other contrasting words could be insincere, deceptive, dishonest, or fraudulent. These words suggest a lack of genuine good intentions and a manipulative or deceitful nature. Additionally, terms like hurtful, harmful, or destructive convey the opposite of intended kindness or goodwill. In short, opposites of "most wellmeant" would use words that suggest negative intentions, insincerity or harm.