opportunistic

This term carries a strong negative charge when applied to human behavior, suggesting a lack of loyalty or a willingness to betray others for personal gain. It evokes an image of someone waiting in the shadows for a moment of weakness in others to strike a deal or seize power. In biological or scientific contexts, the word is neutral and descriptive. An opportunistic infection, for example, refers to a pathogen that only causes disease when the host's defenses are compromised, mirroring the concept of taking advantage of a specific vulnerability.