Not trying to butt in, but here's what God has to say about warning people...
Ezekiel 33:7-16 KJV
So thou, O son of man, I have set thee a watchman unto the house of Israel; therefore thou shalt hear the word at my mouth, and warn them from me.
[8] When I say unto the wicked, O wicked man , thou shalt surely die; if thou dost not speak to warn the wicked from his way, that wicked man shall die in his iniquity; but his blood will I require at thine hand.
[9] Nevertheless, if thou warn the wicked of his way to turn from it; if he do not turn from his way, he shall die in his iniquity; but thou hast delivered thy soul.
[10] Therefore, O thou son of man, speak unto the house of Israel; Thus ye speak, saying, If our transgressions and our sins be upon us, and we pine away in them, how should we then live?
[11] Say unto them, As I live, saith the Lord God , I have no pleasure in the death of the wicked; but that the wicked turn from his way and live: turn ye, turn ye from your evil ways; for why will ye die, O house of Israel?
[12] Therefore, thou son of man, say unto the children of thy people, The righteousness of the righteous shall not deliver him in the day of his transgression: as for the wickedness of the wicked, he shall not fall thereby in the day that he turneth from his wickedness; neither shall the righteous be able to live for his righteousness in the day that he sinneth.
[13] When I shall say to the righteous, that he shall surely live; if he trust to his own righteousness, and commit iniquity, all his righteousnesses shall not be remembered; but for his iniquity that he hath committed, he shall die for it.
[14] Again, when I say unto the wicked, Thou shalt surely die; if he turn from his sin, and do that which is lawful and right;
[15] If the wicked restore the pledge, give again that he had robbed, walk in the statutes of life, without committing iniquity; he shall surely live, he shall not die.
[16] None of his sins that he hath committed shall be mentioned unto him: he hath done that which is lawful and right; he shall surely live.
The Bible also says that "he that knows to do good and does not do it, to him it is sin." That's in James, I think. I don't consider myself much of an evangelist, and frankly I don't do it much. I feel like my gifts lie more in the direction of exhortation (that, encouraging someone in Christ) and counseling. But if God especially tells me I should witness to someone in particular and I don't do it, the blood of that person's soul is on my hands.
The Bible also says, "how shall they hear except someone preaches to them?" Someone cared enough to teach you about Christ so you would know Him and be spared grief in this life and the life to come. So if we claim to have the love of Christ, can we in good conscience ignore a valid opportunity to introduce them to Christ and prevent them from going to hell?
I'll be the first to admit that witnessing isn't my strong point and that I've passed up, regrettably, some excellent opportunities to direct someone toward Christ.
I'll also be the first to admit that if a JW or Mormon comes to my door, I'm likely to ignore them or shoo them off (or prank them. Eheheeheh). But I know that that can also be an excellent opportunity to witness to them, and I bear that in mind if the circumstances permit spending the time to do so (I live in a rural area and have never had a Mormon/JW come to the door, mostly because out here there's a good chance some redneck would shoot one before they ever made it to the door xD I did see 2 JWs in town going door to door the other day, though).
There is a responsibility that God places on each of us to reach people. If we aren't reaching people for Him and living according to His Word, we are classified as "unfruitful branches". And I think most of us know what the Bible says about unfruitful branches.