On the Archdiocese of Washington's blog, Msgr. Pope has a thoughtful post on the deceptively-names moral fault of "respect of persons." Among his examples, he lists the common problem of the self-editing homilist:
A pastor of a parish has a mandate from God and the Church to preach the whole counsel of God. But over the years he has struggled to preach the hard things. After all teaching on things like abortion, fornication, divorce, contraception, homosexuality, euthanasia, Capital Punishment, and so forth, causes some people to be upset. He fears this anger, he fears offending people, he fears being misunderstood.... He chooses to preach only in abstractions and generalities. It is enough to exhort people to be a little more kind, a little more generous, but specificity he avoids. He does this because he fears man more than God. That God might be displeased that his people are not hearing the truth on the important moral issues of the day, or receiving proper instruction in the disciplines of discipleship is a vague and distant fear to this priest. But one person raising an eyebrow at what he says is enough to ruin his whole week.
I doubt you can avoid raising a single eyebrow without lowering a whole lot of eyelids. But let me offer this partial defense of the pusillanimous pastor:
First, I question how well suited the homily, as currently understood and practiced, really is for providing "proper instruction in the disciplines of discipleship." The General Instruction of the Roman Missal instructs that the homily
should be an exposition of some aspect of the readings from Sacred Scripture or of another text from the Ordinary or from the Proper of the Mass of the day and should take into account both the mystery being celebrated and the particular needs of the listeners. 
By design, then, the homily is to be constrained by the other words read at Mass, as well as by the disposition of the audience -- which, in general, includes plenty of bruised weeds and smouldering wicks (to say nothing of young children).
Relatedly, and meaning no disrespect toward our priests, I question how many homilists could do a decent job homilizing on a tough issue anyway. Think about the quality of the last homily you heard on, say, forgiveness or humility, the sort of subject no one objects to hearing about in church. Would you expect the man who gave that homily to give an effective homily -- meaning one that, on the whole, does more good than harm -- on, say, contraception?
Still, I'd guess that a bad homily on forgiveness is likely to be better than a bad homily on contraception, so I can understand why a homilist might choose the former rather than the latter (quite apart from the frequency with which these themes are suggested by the readings).
Finally, one of the reasons effective homilies on contraception are likely to be thin on the ground (improbable, perhaps, even as a percentage of homilies on contraception) is that the reception of a hard lesson depends greatly on the authority of the teacher. Gone are the days in which the laity grants the pastor authority simply by virtue of his office. (And let's say nothing of the freshfaced baby priests.) Achieving the level of authority required to impart a message the laity aren't predisposed to receive is not easy to do, particularly when a priest is only around for three or six years.
The above are reasons it may well be prudent, in the circs., for a homilist to avoid a third-rail homily. Fearing man more than God is not such a reason -- although, I suppose, if a man rightly understand that he does fear man more than God and would therefore make a complete hash out of an attempt to preach against his listeners' wishes, then maybe he should work on his fear of God before working on his homily against contraception.
I still get a kick out of Blogger's spell-checker flagging "homilist" and recommending "homeliest." There's a lesson in homility there. ("Homility" is the feeling felt by the priest in the old story: After Mass, old Mrs. O'Malley told him, "That was a lovely homily, Father," prompting him to say, "Thank you. I just try to let the Holy Spirit speak through me," to which she answered, "It wasn't that good.")