This debate is about smoking in the United States. Pro must persuade you to criminalize the smoking of all plants except marijuana. In contrast, I must persuade you to allow smoking of at least one plant other than marijuana. The resolution doesn’t require that I support the smoking of tobacco.
That said, my case is simple: (1) legalization protects human dignity & freedom of choice; (2) criminalization is hopelessly impractical; and (3) in some cases smoking provides more benefit than harm. Each argument negates the resolution independently. Together, they form an overwhelming case against criminalization.
Before I dive into my arguments, let me briefly address some big picture issues with Pro's case. First, Pro focuses entirely on the smoking of tobacco, which isn't enough to meet his BoP. While tobacco smoke is relevant, it's not the only type of smoking at issue. Pro must persuade you to criminalize the smoking of all plants except marijuana, and on that front, Pro hasn't said anything.
Second, Pro repeatedly misrepresents his own sources. For example, Pro states: "Studies have found mere regulation, even on the FDA's side, are ineffective in comparison." But Pro's source actually says the opposite of his claim -- that criminalization is ineffective when compared with regulation. In fact, the whole study is about how "nicotine regulation" helps, whereas "criminalization" is "hopelessly impractical."  Because Pro's claims don't match his sources, be very cautious about trusting Pro's claims.
Third, Pro's plan is too vague. Will he ban the manufacture & distribution of tobacco? What about other plants that people might smoke? How will Pro get his legislation passed? Or courts to uphold it as constitutional? Or local governments to enforce it? What's the criminal punishment? Will it depend on the type of plant you're smoking? Will Pro imprison the 90% of habit smokers who fail to quit despite trying? Pro needs to specify more details so that I'm not arguing against a constantly moving target.
Freedom of choice. The United States was founded on the principle that individuals should have all the freedom they want to pursue their own views of the good life -- up to the point where an unwilling person could be harmed. This idea is captured by John Stuart Mill’s “harm principle,” which holds that “the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others.”
We adopt this principle for three reasons. First, the harm principle protects human dignity by upholding our inherent ability to choose our own actions & beliefs as well as our ability to take personal responsibility for our choices.
Second, the harm principle maximizes utility because it lets individuals weigh the costs and benefits of incommensurate goods subjectively. Concepts like pleasure & harm are inherently subjective, so the best way to maximize them is by letting individuals weigh them subjectively, as long as those actions don't harm anyone else.
Third, the harm principle establishes political legitimacy by offering a rational basis for leaving a “state of nature” where individuals are free to do whatever they want. We create government (and give up some freedom as a result) to protect ourselves from being harmed by others, and this in turn establishes the limits of legitimate government interference.
Under the harm principle, the government should allow smoking as long as it doesn't harm an unwilling person. The government's job isn't to ensure that people never harm themselves, but rather to protect freedom of choice and human dignity. That's why suicide is legal even though it leads to death with infinitely greater certainty than smoking.
Hopelessly impractical. The reality is this: people will continue smoking regardless of what the law says or how harsh the punishment is. The historical evidence shows that smokers continued using tobacco even when faced with "execution, disfigurement, exile, and onerous taxation" by "monarchs from England to China." Even today, smoking persists in places with strict prohibitions, including in places with religious Mormon & Islamic prohibitions. 
Pro himself admits that 1/3 of smokers don't want to quit despite knowing the harms of smoking, and that 90% fail to quit each year despite trying. Most smokers will probably continue smoking under Pro's plan, which means the harms Pro identifies continue in his world. Even worse, Pro wants to imprison addicts instead of helping them with rehab. But Prisons don't stop addicts from buying cigarettes on the black market.
Indeed, when you criminalize a market with an addicting product, it quickly becomes a black market with everything that entails. The illegal drug trade offers a cautionary tale. Dealers charge monopoly prices -- in prisons, black market dealers charge a 45,000% markup on cigarettes -- and that means smokers have less money leftover to spend on other things, including health.  This will magnify health costs because less smokers will have the money to take care of themselves or to actually pay their healthcare debts. It'll even drive some smokers to homelessness, prostitution, or property crime, simply to afford a smoke. The impacts will likely disproportionately impact Blacks and Hispanics, and it could also increase tensions with the police, further undermining public trust in law enforcement and spurring more unrest & even rioting.
Meanwhile, the higher-ups in gangs and drug cartels will reap enormous profits from cigarette sales, and they will use this money to fund terrorism, political corruption, and other destabilizing tactics. Studies predict that a total smoking ban would fuel already-existing tobacco-based cartels and other drug cartels, leading to a massive increase in violence and terror.     And that still leaves all the harms we can't predict ahead-of-time. Maybe Pro's plan will decrease high school graduation rates because it increases illegal opportunities for dropouts in the black market? Who knows?
Criminalization also poses a money problem. States raise a lot of money by taxing cigarettes & other smoking material. How will Pro's plan replace this lost revenue? What about all the lost jobs related to the tobacco industry? How will governments pay for new police expenditures, judicial expenditures, and prison expenditures? Even non-smokers don't want to criminalize smoking because they don't want to pay for government enforcement of a lost cause, nor do they want to pay for lost tax revenue. In effect, Pro wants non-smokers to subsidize a black market.