I am all for medical marijuana but if one is just a stoner and has to smoke pot just to get through the day, they are of little use to EMS. Other professionals are held responsible for their behavior. Why should EMS be the poor pathetic ones that everyone should cut some slack? Could it be because some do give off the impression of being exactly as you described rather than that of a health care professional?
Also, if you smoke cigarettes, you are not going to work for many FDs, EMS companies, hospitals or a whole lot of other employers.
Cigarettes aren't altering any more than being addicted to ice cream is...unless the two have brain freeze in common. On the other hand, ice cream doesn't leave a stink on everything it comes in contact with like tobacco does. <_<
On the more serious side; no state is going to issue an EMS license to a candidate who requires mary-jane to function. Not even the Americans with Disability Act can support a person under the influence of a medication with a high potential for creating an unsafe situation for the worker or those around him/her. No employer is required to keep such an employee either.