Those modern conservatives you're talking about are what we generally refer to as neocons (neo-conservatives) and they don't adhere to the basic precepts of conservatism - a small, defense-minded government with low taxes that favors utilitarian efficiency. "Legislating their morals," as you put it, increases the size of the government - which goes against the "small government" part of the traditional conservative approach.
Hopefully most neocons will eventually realize their intrinsic error and will revert to traditional conservatism, because it is the balance between real conservatism and real liberalism that keeps our government moderate. As the Democratic Party has shifted to the left over the years, so has the Republican Party - but the larger government under these left-leaning Republicans has been structured for favor their constituents. A bigger, yet business- and religious-oriented government is sure to get most liberals' hackles raised - hence the huge split between the parties that we've been seeing lately.
You can't totally blame the neocons for this; their shift left was an attempt to keep the divide between the two parties from getting too big. Unfortunately, that shift left encompassed only the political part of the spectrum, so the divide occurred anyway. And now we're living with the result - two political parties that are extremely confused about what they're supposed to stand for and how to proceed from here.
Anyway, that's how I view the situation. There are a few holes in the logic but that's just how that works sometimes.
