Yes missionaries when they are biblical and godly find that the nations do not deserve the gospel. But they also find that we ourselves who have been found in Christ did not deserve the gospel. But God loved us and we now find that we must love as we have been loved.
The missionary enterprise of the church is fraught with danger. Persecution, malaise, a willingness to tolerate false teachers from within and disputes between believers. But the promise still remains. The gates of hell will not hold out the gospel
And when we stand before God in judgment we will say what the hymn writer sang. “Nothing in my hands I bring, simply to thy cross I cling. That’s the gospel. And that must be shared with all the people of the world.