Coincidentally, when preparing for my political theory exam the other day my friend was pondering a similar question, and proposed that patriotism may be inconsistent with liberalism insofar as it violates state neutrality. That is, the liberal believes the government should stay away from doing anything controversial that some citizens may disagree with, and any self-congratulatory formal celebration sessions promoting the idea of the nation seem to be an example of the state doing precisely that.
Of course, this would just mean the government shouldn’t promote patriotism. It wouldn’t mean liberal citizens couldn’t voluntarily be patriotic. But I imagine an explanation of why liberals tend to avoid such activities lies in our rationalist mindset: we believe in cold, cautious observation of government, and thus show little need for the kind of sentimentality inherent to waving flags. It is a fundamentally conservative act: a fine example of the type of institution that reflects the ties that bind us and the liberal is allegedly blind to. This may even go some way, for instance, to explaining the disconnect between people like Greenwald and Sullivan on the issue of emotion in politics.
But it seems to me there is at least one form of patriotism that is perfectly consistent with liberalism, both in the sense that liberal citizens should embrace it and liberal governments need not shy away from it. Namely, a patriotism focused on celebrating the liberal state itself. If when flying the flag, what is going on mentally is a celebration of fundamental liberal principles like equality, and core freedoms such as that of thought and speech – what could possibly be illiberal about fostering those sorts of feelings?
And I think this sort of thought is intrinsic to and dominant in the American identity. It is reflected in their other key national symbol, the Statue of Liberty. So perhaps Britain is at a disadvantage here. As we know too well, our flag is too tied up with the monarchy and football. But maybe British liberals should get to work on changing that.