I have been listening to a droll and informative lecture by Daniel C Peterson, who is a well-known Mormon scholar (and pundit) on the subject of using the internet to promote and defend Mormon Christianity.
He gives a good picture of the scope of the internet, and the new possibilities; balanced by a hard-headed appreciation of the limitations of traditional/ conventional missionary attempts - ringing doorbells, accosting people on the streets.
A few of his suggestions are:
1. Respond to interest, rather than cold-calling, Anyone who comes and asks about Christianity is much more likely to respond than a random individual - who may be annoyed (quite reasonably!) by an approach from a stranger.
2. Don't always be defending against criticism and ridicule; (if asked) sometimes it is better to emphasize the positive - especially if it is personal (explain, honestly, why you personally are Christian - what the faith gives you that you need).
3. The secular world often sees devout Christians as boring people, and Christians unwittingly may exacerbate this by always trying to reassure; therefore it may be better not to hide or downplay, but rather to emphasize upfront the 'strange' aspects of your faith, the supernatural, the distinctive etc.
4. Practice Triage - because your time and efforts are finite. Some people don't need apologetics and with other people it is a waste of time because they are not serious or not ready or have malign intentions. Direct your efforts where they are most needed and most effective.
This point about triage struck a chord, because I often see blog commenters who are, I believe, deliberately wasting the finite time of Christian bloggers (i.e. 'trolling') - and in the process making the comments section repulsive and inhospitable to those who might benefit from it.
This kind of thing may be a calculated anti-Christian strategy - and it is really quite common. I have also seen it in 'real life' as well as the internet.
The answer is straightforward - don't let trolls dissipate your finite time and effort, and don't let trolling spoil the pro-Christian environment you are trying to create; don't let those who are (currently) beyond help, prevent your encouraging and helping those who might most benefit.
Make a judgement - and if you believe that trolling is afoot, ban them from the venue!
You may get it wrong, but the failure to triage swiftly and effectively may be much more serious than an error in triage.
Of course 'trolls have souls' - but a ban might well be good for them! It is not helpful if Christians always behave like gullible idiots - and acts of insightful, realistic, tough-mindedness from Christians may sometimes be the most effective 'argument'.