I believe scripture teaches us that there are evil people. It states that they hate the light of God and they will not come to the light of God. (John 3:20; Job 24:16; Jeremiah 9:6) It's not an inability, it's a refusal. They have set their hearts to walk in darkness. Who knows why. It's a product of their self will, a product of human pride. Regardless, they actually like to do evil and they don't want God's light to expose them.
That said, our problem arises because we cannot see a person's inner heart, only their outer actions. It took a direct word of God for Ananias to go to Saul; all he could see is a man persecuting Christians. (Acts 9:13-15). We are not God; therefore we cannot judge whether someone can be saved or not. Our job is merely to share God's love as demonstrated by Jesus Christ. And this flows from within us, not out of a sense of duty, but out of the compassionate heart of Christ that dwells in us. This is why we need to draw closer and closer to God through Christ, allowing him to change us, allowing him to make us more and more like Christ. For when we surrender our lives to God in this way, our care for other's souls will be such that we will never refuse to give anyone the gospel.
The sharing of the gospel is our part of God's work. It is the privilege he is a given to each one of us.. God's part is to take that word to their heart. Their part is to accept it. But, sadly, despite our efforts --and God's-- some, being evil, will reject not just the gospel that can save them but the God that made them.