Maybe you've heard the arguments that witnessing to the lost is (a) in the same category as alerting your neighbor if their house is burning, and (b) part of your Xtian duty in "loving your neighbor as yourself." I disagree.
First of all, if my neighbor's house is burning, there's absolutely no condemnation involved towards him in my alerting him. In contrast, when I tell my neighbor about God's holiness, man's sin and God's wrath, the neighbor feels "judged." (Whether he's right is another issue; they always misconstrue that pt.) Furthermore, it is an objectively verifiable fact that neighbor's house is burning (he can call another neighbor to confirm it), whereas God's wrath and our sinfulness and need for Christ's atonement/righteousness are not objectively verifiable.
Secondly, I myself hate it when Mormons or JW's try to get me to believe their falderol. I resent not only the lies they propound, but even just their gall in knocking @ my door (or coming up to me when I'm taking my walk or sitting in the park). So why would I then want to behave that way towards my neighbor the unbeliever? Why would I presume to foist my beliefs on him if he hasn't asked to hear them? (See my previous post about this last aspect.) And no, don't go using the "planting a seed" rubbish on me: the seed will be useless and die unless the ground has already been prepared (in which case [again, see my previous post], the unbeliever will probably show some sort of interest in discussing spiritual matters). Even worse, the seed might get caught in the guy's craw and cause him to close up to future "witnessing."