In Matthew’s usage, “fulfill” has a fuller sense (if you’ll pardon the expression) than just the Micah 5:2//Matthew 2:5-6 predictive prophecy usage. For example, the Hosea 11//Matthew 2 usage is real fulfillment, but it’s not predictive prophecy. The Hosea passage is not a prediction of the future Messiah, but a reflection on Israel’s history: “When Israel was a child, I loved him, and out of Egypt I called My son.”
The original sense in Hosea is critical to Matthew’s meaning. Knowing that Israel is God’s son is necessary to understanding the points that Matthew is making: first, that Jesus is Israel (in a meaningful sense that Matthew will spend the whole book exploring), and second, that the land of Israel has become spiritual Egypt – a point that will be reinforced by John the Baptist when he calls the remnant out into the desert to pass through water.
We don’t want to read something into the text that isn’t there. At the same time, we don’t want to miss something that *is* there—and the NT shows us repeatedly that there’s a LOT more there than one might think at first glance. From Jesus Himself proving the resurrection by exegeting a verb tense in Genesis (Luke 20:37-38) to the fulfillments of the first few chapters of Matthew (1:22-23, 2:15, 17-18, 23) to the dizzying displays of Hebrews, the NT shows us a way of reading the OT that we wouldn’t have come up with on our own. It had to be revealed to us.
In conservative circles, we have gotten our hermeneutics from the Book of Nature (mostly as read by E. D. Hirsch), which is very useful as far as it goes. But God wrote two books–God’s Word and God’s world–and the Book of Scripture also has something to teach us about how to read well. We should not refuse to learn that set of lessons as well.