The muslim suicide bombers are sure they're going to Heaven and they're sure they're doing the right thing.
So?
You're right.
The Romans thought Zeus and others were gods. They were wrong. They are both examples of false teachings.
Jesus said, "I am the way, the truth and the life...no one comes to the Father but through Me (John 14:6 NASB)."
The way the Greek is set up on the "I am" part of this statement essentially means compared to all other beliefs, Jesus is the only way to the Father.
All other ways are false.
We have Papists who are positive that salvation is through the Roman Catholic Church even though their "infallible" magisterium is filled with sodomites and leftists who have been changing even their own theology right beneath the true-believers' dumb noses.
You should get a load what crap your church teaches even in their approved biblical commentaries, and you guys want us to kneel and scrape and beg for salvation from you guys when most of you aren't capable of much more than very basic and puerile apology in defense of your works-righteous doctrines?
Come now, I'll stick with the holy scripture, and sit at rest with Luther, with Calvin, with John Knox, with the tens of thousands of Christians who have been martyed for their faith, and with Augustine, and Chrysostom, and so many others, on the essentials of the Gospel. You guys don't even have the essentials anymore.