Final answer:
The opposite of 'insidious' might be 'benign' for harmlessness or 'overt' for openness, with both terms being antonymous to aspects of 'insidious' either in intent or method of operation.
Step-by-step explanation:
The term insidious refers to something that proceeds in a subtle way but with harmful effects. In searching for the opposite of 'insidious', you would be looking for a word that describes something that is direct, benign, or perhaps even beneficial in its approach. The antonym you might consider is benign, which suggests something that is gentle, not harmful, and does not spread in a stealthy manner. Another suitable opposite could be overt, which means open and observable, not secret or hidden. Here the focus is on the lack of stealth rather than the potential for harm.