Whether this is so or not depends on whether you are assuming hedonistic or preference utilitarianism. For a hedonistic utilitarian, contraception is, in a sense, tantamount to murder, except that as a matter of fact murder causes much more suffering than contraception does, both to the person who dies, to his or her loved ones, and to society at large (by increasing fear). By contrast, preference utilitarians can also appeal to the preferences of the individual who is killed: whereas murder causes the frustration of an existing preference, contraception doesn't, since nonexisting entities can't have preferences.

The question also turns on issues about population ethics. The previous paragraph assumes the "total view": that people who do not exist but could or will exist matter morally, and just as much. But some people reject this view. For these people, even hedonistic utilitarians can condemn murder more harshly than contraception, wholly apart from the indirect effects of murder on individuals and society. The pleasure not experienced by the person who fails to be conceived doesn't count, or counts less than the pleasure that the victim of murder is deprived of, since the latter exists but the former doesn't.

For further discussion, see Peter Singer's Practical Ethics, chap. 4 ('What's wrong with killing?").