I agree with Dr. White that the basic moral principles Kant endorses – specifically, the prohibition on treating persons as mere means – commit him to a broadly libertarian politics, and that Kant follows out the implications of that commitment to a considerable extent. But I’m less convinced by White’s attempts to downplay the centrality of some of Kant’s deviations from those implications.
Specifically, White acknowledges that the passage I cited from the Doctrine of Right “appears to endorse a system of coerced redistribution,” but he suggests that its “tone and content are in striking contrast to Kant’s more general statements regarding the narrowly circumscribed domain of state coercion (to limit coercion by others).” Here I disagree. It seems to me that Kant is thinking in Rousseauvian terms here: since all the individual property-holders are to be regarded as parties to the (fictional) social contract, the political disposition of their property is (as Kant sees it) in an important sense not coercive, since they’ve all agreed to have their individual holdings regulated by themselves in their collective capacity (as represented by the state).
The problem Rousseau faced was that of reconciling political authority with human freedom and equality. His solution was the idea that in the social contract, we all individually submit ourselves to all of us collectively, so that (so long as the collective rules in accordance with the general will) we are subordinated only to ourselves and so remain technically free. Through this “total alienation of each associate, together with all his rights, to the whole community,” says Rousseau, “each gives himself absolutely,” and since “the conditions are the same for all … no one has any interest in making them burdensome to others”; thus “each, while uniting himself with all, may still obey himself alone, and remain as free as before.”
And here is Kant in high Rousseauvian mode:
The legislative authority can belong only to the united will of the people. For since all Right is to proceed from it, it cannot do anyone wrong by its law. Now, when someone makes arrangements about another, it is always possible for him to do the other wrong; but he can never do wrong in what he decides upon with regard to himself (for volenti non fit iniuria [= “to the willing, no injustice is done.”]).
Thus on Kant’s view, when the state redistributes its citizens’ property, it does them no injustice, since the actions of the legislative authority are simply the people acting upon themselves.
This Rousseauvian approach pervades Kant’s political thought (albeit uneasily interwoven with Lockean and Hobbesian strands). For example, Kant’s justification of marriage is a Rousseauvian social contract writ small. For Kant, sexual intercourse is presumptively immoral, since it involves using one’s sexual partner as a means to one’s own pleasure. (He seems unaware that people sometimes try to give their sexual partners a good time as well. But then his personal experience in this area was not extensive.) The institution of marriage legitimizes the sex relation through a contract involving subordination that, in virtue of being reciprocal, in a certain sense ceases to be true subordination (even though the male spouse is the sole government of this mini-republic).
There is nothing surprising, then, in Kant’s taking redistributive taxation to be noncoercive, insofar as the state is to be viewed, not as violating its citizens’ property rights, but as exercising those rights on their behalf. This is the vicarious conception of consent that I referenced in my initial essay, and it is pervasive in Kant’s political thought (even if it has to share space with a more immanent conception congenial to libertarians). And in fact he is getting it straight from Rousseau, whose account of property in The Social Contract likewise sounds rather Lockean (with its talk of first occupants establishing property rights through labor) until Rousseau reminds us that proprietors, in order to render their holdings more secure, surrender those holdings entirely, along with themselves, to the collective sovereign, whereupon the united private holdings constitute a “public territory.” In J. L. Austin’s words, “[t]here’s the bit where you say it and the bit where you take it back.”
Moreover I do think that the sharp opposition, in Kant’s ethical thought, between our true will and our mere inclinations makes it easier for Kant to find his way to a vicarious, Rousseauvian approach to consent – just as his division between the noumenal and phenomenal realms makes it easier for him to embrace a fictional social contract that devalues real consent in favor of a merely posited consent. (After all, Kant’s view of free will is that we are pawns of causal determinism in the phenomenal realm but must think of ourselves as being free agents in the unknowable noumenal realm. If the move works for moral freedom, why not similarly for political freedom?)
The Lockean strand in Kant’s political thought is real and important. But it stands forever in the shadow of the Rousseauvian strand, which lies ready at any moment to devour and transmogrify it.
 Jean-Jacques Rousseau, The Social Contract I.vi: http://oll.libertyfund.org/titles/638#Rousseau_0132_124
 Kant, Doctrine of Right II.1.46, p. 125/313.
 Rousseau, Social Contract I.ix: http://oll.libertyfund.org/titles/638#lf0132_label_0690
 J. L. Austin, Sense and Sensibilia, ed. G. J. Warnock (Oxford: Oxford University Press, 1964), p. 2.