Perhaps I do, and perhaps I don't. But I'd prefer we discuss the issue than my general view of the world.
Let's take your scenario: someone is on the brink of starvation, and an opportunity to sell drugs (and not starve) falls in their lap. They take it (without any prior plan). This is definitely opportunistic.
What happens if the above situation is repeated a second time? Do we consider that opportunistic as well?
How many times does someone have to take such an opportunity before we consider them selling drugs as being 'what they do' or part of their plan?
Unless the chance of being arrested is close to 100%, it's unlikely that someone's first arrest for selling drugs coincides with the first time they sold drugs. So is it really opportunistic?