Rom 10:14 How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher?
Rom 10:15 And how shall they preach, except they be sent? as it is written, How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things!
I daresay that Christ would not spit my efforts out of his mouth as they are done in seeking to glorify Him. The lukewarm-ness to which you refer (from Revelation) describes the [absence of] love found in the church of Laodicea. It is my very love for Him which I seek to manifest to the lost. That it is done in a godless institution, that it may reap little or no positive results, it nevertheless demonstrates to the Lord my love for Him. That it doesn’t measure up to your standard of a testimony is irrelevant. It may be that by testifying to the Lord in whatever way s/he can, the Christian teacher working in the government schools of today do just as much as any foreign missionary. Do you think missionaries working overseas simply go out and overpower one culture with another? No. They go out, join themselves to a people, live a Godly example before them and then, as occasion arises, are able to give a word, in season, concerning their faith. Paul would say, “But now, I show you a better way...”
Now, on the other hand, those that would withdraw from the spiritual warfare, attempt to set up their own little “private Eden” somewhere and then wait for the world to discover its eternal bliss somehow may be the ones who will have to give an account as to the burying of their 1 talent. That’s not for me to say; that’s up to the Lord. The Christian teacher is taking their 10...or 5...or 1 talent and trying to gain 10/5/1 more for the Lord. That you do not see this as anything but a negative is puzzling...or don’t you believe that the Lord can use even the (few) opportunities that present themselves in the public schools of this country to further His Kingdom through His instruments on school faculties? I have had more opportunities to share my faith in the schools where I have taught than most Christians have had—without being disobedient to the laws of the land or the Lord of Glory.
Teachers who agree to establish, support, and run godless schools are **willingly** creating spiritual wastelands. They agree, even seek, to run the godless government camps that spiritually starve children.
True missionaries wouldn’t do that.