And this is why people who want good for themselves and others (especially those around them) use good judgment and care about what they take in via the senses; especially eyes and ears. It will affect (or infect!) the mind and intelligence (meaning the part of our consciousness that directs the mind) and thus our speech and actions.
As the Bible records: A man is not defiled by what enters his mouth, but by what comes out of it. Matt 15:11