The problem isn't earmarking funds in general. Money has to be allocated somehow and it's good to do so explicitly.

The problem is earmarking or allocating a variable set of revenue as funding for something unrelated, and in particular something unrelated that's otherwise valuable or important.

And NOT earmarking or allocating 'sin taxes' to pay for the supposed costs of those sins, borne by the public in the form of the government, seems pretty stupid (to me) if it's actually necessary or desirable for the government to 'manage' those sins or those sin's consequences.