I used to struggle a lot with this one myself. But, now I've come to recognize the wisdom of what Jesus was telling us here. While it doesn't happen here on this forum, I've found many times on forums that allow atheists and other non-believers to be members, that there are some who are simply going to argue and ridicule our faith. You can patiently explain things, lovingly answer questions and open yourself up, just to get smacked down.
Praying for discernment does help. Sometimes someone can seem as though they are there just to ridicule, but then days, weeks, months later come back and really begin to search. So, as long as the Holy Spirit leads, I'll go ahead and put up with a certain amount of 'smacks'.
But, I've dealt with those who really do just trample God's Word to them. If all they want to do is ridicule, then there is no point in continuing on with trying to share. As a matter of fact, it might be more detrimental to ultimately winning them, to allow a continued disrespect. As I so often tell my daughter, "Nobody will respect you more than you respect yourself." By upholding the gospel and God's pearls as worthy of respect, we also speak to the unbeliever about how important it is.
All in all, it is not our words that is going to convict anyone, it is the Spirit.
And, I agree wholeheartedly with the fact that we can and should always pray!