No, there isn't any reason why the Internet couldn't be used to tell people about the Gospel of Jesus Christ - which is exactly why we are using it in every way we possibly can! (You can visit us on the Internet at billygraham.org.)
In fact, our organization is involved in a coalition of Internet ministries from various parts of the world, working together to explore new ways to use the Internet for evangelism. You're right, of course; the Internet can be used to promote great evil - pornography, fraud, hate, racism, and so forth. But the same is true of every other form of media - books, for example, or films. In the right hands, however, the Internet is a tool God can use to promote great good, and even to bring people to Christ.
One of the most interesting facts to me about the Internet is that it now reaches some of the most remote corners of the world - including countries that are otherwise closed to the preaching of the Gospel. I can't help but think of Jesus' words concerning what will happen before His second coming: "And this gospel of the kingdom will be preached in the whole world... and then the end will come" (Matthew 24:14).
Pray for us, and for all who are seeking to find new ways to reach our world for Christ. Pray too for those who are coming to Christ every day through the witness of others on the Internet, that they may find fellowship and grow strong in their faith.