Assume that information wants to be free. Furthermore, that it wants to be organized and easily searchable by anyone in the world. Or at the least, that there are sufficient forces at work to make that happen. This can be seen as a irreversible trend manifested by the very advances in technology that we love.
Now, if you start with that assumption, you can also assume that Bad People will have this wonderfully organized data and will do Bad Things with it.
If you make that leap, then you can, as a government, see why you would want All The Data on the Bad People so that when they inevitably do the Bad Things, you can catch them.
Now, assume all the above and figure out your place in this world that will manifest for our next generation.
For example, I generally assume that by the time my kids are my age, genetic sequencing will be common and cheap and probably also done without permission (think Gataca). It will be done by Bad People and will also be done on everyone by our government in the name of catching the Bad People. It isn't what I want, its just what I expect to happen...