On most major campuses there is absolutely no danger in being anti-prohibitionist. Have a no-smoking rule at your meetings. This reduces the danger and increases your credibility. Non-smokers will be more comfortable joining. If the only reason that they join is to be able to smoke at meetings, you don't need them.
People can smoke afterwards.
Work on your communication skills, writing and using the Internet. Tell people that you meet on line about anti-prohibitionist web sites. Write letters to the editors of papers that publish reefer madness articles. You can ask that they not use your name because anti-prohibitionists don't have First Amendment rights in your area. That may make them think a little.