I don't believe it’s the only way. Go ahead and look if that's what you think you need to care. But how can you not already understand that other people are real?
Back in the 1960s, we only needed to see footage of black protesters being beaten, hosed down and attacked by police dogs once to understand how bad racism was down South.That's a different use of "only." It is enough to see pictures sometimes (though pictures, even moving pictures, can deceive). But that doesn't mean that pictures are the only way to learn what evil is, what suffering is. And we fall short if only pictures work for us. Indeed, we are open to manipulation if that is our sole method of learning.
I'm reminded of words from another context:
"Because you have seen me, you have believed; blessed are those who have not seen and yet have believed."