The best argument against it is: it's very hard to enforce it on everybody internationally, and if one country adopts it unilaterally, then production just moves to another country (making everyone worse off - same amount of pollution, but the production is presumably less economically efficient).
The second best argument against it is "the tax shouldn't be $x/ton, it should be $0.5x, which is a more accurate reflection of the external costs".
A distant third, but very effective in practice, is "the carbon tax is good, but it shouldn't apply to Special Interest Area X, because of these social/political/historical reasons..."
These aren't completely unsolvable problems, and people do try. But if your question was genuine, I hope you now see that there are some reasonable arguments not to just do this tomorrow.