Kant's categorical imperative is an expression of the bourgeois liberal ideas of the 18th century, expressed as morality. It is progressive in the sense that it attempts to derive morality from Reason. It is part of the Enlightenment. It also expresses the new, universal promises of the bourgeois revolutions in that it universalises (i.e. "All men are created equal"). It is based on the principle of universality. What you do must apply to all people or it fails to be truly moral.
However, it is also based on a bourgeois notion of rights. The concept of 'rights' is a product of the rise of bourgeois property/trade relations. One brings one's rights to the market place and, on that basis, one participates in the putatively level playing field. For Kant, one negotiates the conflicts between these rights on the basis of contractual clauses. If the Party of the First Part undertakes to do such and such, the Party of the Second part will be understood to be obliged to do so and so. It is this which finally inverts the universality of the notion into an entire bourgeois conception of individualism. Through this embedded notion of contractual obligations, the decision as to universal moral actions rests with the individual's willingness to enter into a personal contract regarding his conduct, his willingness to be bound.
The sting in the tail lies in the fact that different people will always have different notions as to what is or isn't universally desirable. One individual may consider it highly desirable that theft be considered universally immoral because they have a great personal interest in the institution of private property (i.e. because they own lots of it). Another (who perhaps owns little) may be prepared to risk universalising the permissability of theft if he thinks he can steal what he wants and then protect his stolen goods by force. Alternatively, there may be those who feel that there are worse prospects for the future than the fall of private property. And, in practice, the guardians of morality will always be ready to claim the universality of laws that they themselves break, simply because they take a more pragmatic view of Reason.
The R/reasonable promises of bourgeois liberalism and Enlightenment will always have such loopholes in their social contracts and, as a result, will always find themselves in full or partial, official or unofficial abeyance. The Enlightenment declared that all men were created equal, but oversaw (and, indeed, was partially built upon) all black men (and women) being crated equally... for shipping. Why should a white man who profits from the slave trade care if 'enslave black people' became a universal moral maxim? He knows the colour of his own skin will exempt him from the chains, and the inequality of property and opportunity will protect him from universal business competition.