The official Colorado staff analysis says:
"Even if Amendment 64 is adopted, the possession, manufacture, and sale of marijuana remain illegal under current federal law, so the adoption of the measure may expose Colorado consumers, businesses, and governments to federal criminal charges and other risks. People who invest time and money to open marijuana establishments have no protections against federal seizure of their money and property. Because federal banking laws do not allow banks to accept the proceeds of, or loan money for, activities that are illegal under federal law, marijuana businesses will likely need to be cash-only businesses. In addition, enhanced federal scrutiny and competition from retail marijuana establishments could jeopardize the existing medical marijuana system. The efforts of individuals who feel that marijuana use should be legal for all adults are more appropriately directed at changing federal law."
"Marijuana impairs users' coordination and reasoning and can lead to addiction. Allowing state-regulated stores to sell marijuana will make it more accessible, which is likely to increase use and may give the impression that there are no health risks or negative consequences to marijuana use. Greater accessibility and acceptance of marijuana may increase the number of children and young adults who use the drug. Furthermore, because more people are likely to use marijuana, the number of those who drive while under the influence of or while impaired by the drug may increase."
"Amendment 64 asks voters to approve a regulatory structure for the sale of marijuana, but does not specify critical details about what the regulations will entail. Furthermore, because the provisions of Amendment 64 will be in the state constitution and not in the state statutes, where most other business regulations appear, there may be unintended consequences that cannot be easily remedied. For example, the state legislature cannot adjust the deadlines, fees, and other details regarding the implementation of the measure. In addition, by constitutionally permitting marijuana use, the measure, despite its stated intent, could create conflicts with existing employment, housing, and other laws and policies that ban the use of illegal drugs."