Well, they aren't teaching that you can't preach that, love, peace and joy are one of the greatest gifts our saviour gives. But you can't deny the other facts while teaching it.
Some people teach that they have love, peace and joy from Christ yet they continute to live in sin. That is hypocritical living at it's finest.
You have to teach the full gospel, not just have of the gospel. It is the full gospel, the full meaning that has the highest impact.
Do we go through our lives, telling half truths? Not too likely, so why would we only share half of the gospel?