The common interpretation is that the basket of apples is an analogy for your beliefs, opinions, and perspective.
It’s possible that one or more apples are rotten. Who cares, right? Does it matter if there’s one rotten in a mass of healthy?
Yes. It matters. Decay is like an infectious disease and if you don’t remove the foul apple, it might infect the healthy apples around it.
We can’t look at beliefs and opinions isolated and separate from each other. They are connected, one is built on the other and a single wrong belief poses the risk to spread its falsehood within our belief system.