Although your opening statement consists of several "categories," you've really only made three points:
1. Marijuana use is harmful to the health. This is supported by half-truths and myths.
2. Marijuana use leads to the use of other drugs. This is supported by...nothing.
3. Because marijuana use is harmful to the health, it should be illegal. This is supported by dogmatic opinions about the nature of marijuana smokers, and the unfounded assumption that marijuana laws actually influence the rate of its use.
I will address each of these in turn.
1a. Marijuana is more malignant than cigarette smoking
While I agree that inhaling smoke into the lungs can and probably does cause cell damage and long-term respitory problems, research that suggested a link between marijuana use and cancer has been called into question. By the same researcher no less.
"The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer. The new findings "were against our expectations," said Donald Tashkin of the University of California at Los Angeles, a pulmonologist who has studied marijuana for 30 years. "We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use," he said. "What we found instead was no association at all, and even a suggestion of some protective effect."
Federal health and drug enforcement officials have widely used Tashkin's previous work on marijuana to make the case that the drug is dangerous. Tashkin said that while he still believes marijuana is potentially harmful, its cancer-causing effects appear to be of less concern than previously thought." Study Finds No Cancer-Marijuana Connection 1b. Marijuana causes mental disease such as schitzophrenia, paranoia, and anxiety
This is a myth. The source you provided relies solely on the statistical correlation between schizophrenia and marijuana use. It does not provide any evidence to suggest that marijuana actually causes it. In fact, doctors at the Institute of Medicine agree that marijuana does not cause schizophrenia, and other psychological effects like paranoia and anxiety are unlikely to persist beyond intoxication.
On schizophrenia:
"Regardless of which of these interpretations is correct, both camps agree that marijuana use alone—without the influence of additional risk factors—is unlikely to provoke a psychosis that persists longer than intoxication. Drug abuse is common among people with mental illness. Thus, it is not surprising that several (but not all) studies have shown that a disproportionately large number of people with schizophrenia use marijuana. The association between marijuana and schizophrenia is not well understood, however. While experts generally agree that heavy marijuana use can provoke schizophrenic episodes in susceptible individuals, they also concur that the drug does not cause the underlying disorder. Additional research indicates that people with schizophrenia prefer the effects of marijuana over those produced by alcohol and cocaine, which they generally use less often than does the general population. The reasons for this preference remain unknown, but it suggests that marijuana might give these patients some relief from their symptoms." Marijuana As Medicine?:
On paranoia and anxiety:
"Although euphoria is the more common reaction to smoking marijuana, adverse mood reactions can occur. Such reactions occur most frequently in inexperienced users after large doses of smoked or oral marijuana. They usually disappear within hours and respond well to reassurance and a supportive environment. Anxiety and paranoia are the most common acute adverse reactions" Marijuana and Medicine: 1c. Marijuana creates learning disabilities
1d. Marijuana creates amotivational syndrome
1e. Marijuana creates a mediocre class of chronic smokers
These are all myths. None of the provided links support these assertions, and I am unaware of any scientific research that supports them.
2. When the thrill of marijuana erodes, the next great drug must step into to replace it
This is a myth. None of the provided links support this assertion, and I am unaware of any scientific research that supports it. Furthermore, I already addressed the "gateway drug" argument in my opening statement. Allow me to repeat the Institute of Medicine:
"There is no conclusive evidence that the drug effects of marijuana are causally linked to the subsequent abuse of other illicit drugs." Executive Summary | Marijuana and Medicine: Assessing the Science Base | Institute of Medicine 3. Because marijuana use is harmful to the health, it should be illegal
This statement is dubious for two reasons. First, the notion that any substance which is marginally harmful to the health should automatically be illegal is a slippery slope. Should glazed donuts and coffee be against the law for the same reason? Second, it assumes that laws prohibiting marijuana use are actually effective at reducing the number of users. Again, I addressed that argument in my opening statement, and it was not refuted by any of the sources you provided.
Setting aside the points that I preemptively refuted in my opening statement (marijuana is not a gateway drug and prohibitive laws do not influence the rate of use), we're left with suspicious correlations to health problems as your main argument. Disregarding the fact that the specific health problems you mentioned are not corroborated by doctors at the National Academy of Sciences, there are in fact some legitimate health concerns surrounding the use of marijuana. However, this is a good reason why marijuana should not be used; it is not, by itself, a good reason why it should be illegal.
To help keep us from talking past each other throughout the debate, I would remind you of the points I made in my opening statement and invite you to address them if there is credible research to the contrary. Otherwise we should assume that the points are conceded, and thus further arguments should not be based on assumptions that disagree with them.
Criminal Laws Have Little Effect On Marijuana Use
Marijuana is a Gateway Drug Because it is Prohibited
We Must Choose Between a Black Market and a Regulated Market
Legalization Will Allow Marijuana to be Regulated and Taxed