The biggest problem with preaching about Hell is that these days, no one seems to know the difference between a statement and a threat. If you preach about Hell, most atheists will reply with something along the lines of "threatening me with Hell isn't going to make me believe".
But of course, it's not a threat. No Christian believes they even have the ability to damn someone to Hell, so it wouldn't even make sense to attempt to threaten someone with Hell. Rather, "threatening" someone with Hell is actually just a reminder that Hell exists.
Consider the following analogy. Bill and Ben are arguing about illegal drugs. Bill loves drugs, Ben thinks Bill should stop doing drugs. So Ben tells Bill that he might go to prison. Is Bill justified in responding with "stop threatening me"? Of course not! Ben is right. If you're caught with illegal drugs, you're probably going to jail. Ben is not threatening Bill, Ben is lovingly warning Bill of the dangers of his lifestyle.
Oh, but of course, while Christians aren't threatening people with Hell, isn't God? Let's stick with Bill and Ben, but it turns out the police have the place bugged. So Officer Walker knocks on the door, and the two answer. "Listen, Bill, I'm about a week from retirement, so I'm going to offer you a deal. I know you do drugs, and I have the legal right to bust you for them, but I'm going to offer you a choice. Stop doing drugs, I won't arrest you."
Some of you may have already noticed what I did in this analogy. Bill is guilty. Prison is no longer a threat, it is a fact. But rather than say "don't do drugs or you'll go to prison", Officer Walker offered Bill a generous reprieve. You have done the crime, you are worthy of punishment, but I will let you off if you repent.
Of course, there is a bit of a difference. Officer Walker should have arrested Bill, because that is called justice. Letting Bill off scott free is unjust. But in Christianity, God is perfectly just. Every sin must be accounted for, every wrong must be put right. And so God only had one option: Someone else would have to pay our price. So He sent Jesus to be born of a virgin, live a perfect life, die a sinner's death and rise, having conquered death for Himself, and for anyone who will humble themselves, repenting of sin and confessing Him as Lord, believing that God raised Him from the dead.
It is not a threat to offer us a way out of receiving eternal punishment for a sin we have already committed. Certainly not when there is undeserved reward; eternal life. You are already on a path to Hell, He offers you salvation. That is a generous offer, not a threat.
The ironic thing is, in order for Hell to be considered a threat in the first place, you would have to believe Hell exists. Imagine if a guy with no arms threatened to stab you. If you feel even remotely threatened by Hell, it's because you already know it exists. In this case, complaining about threats makes no sense. Why aren't you rushing to bow to the King of kings? You don't have forever to be reconciled to God. That's not a threat, that's a fact.