Bible Answer: Smoking pot is wrong first of all because it is against the law in the United States. Even where some states have legalized it, the federal government does not recognize those state laws.

Paul wrote: "Everyone must submit himself to the governing authorities, for there is no authority except that which God has established. The authorities that exist have been established by God. Consequently, he who rebels against the authority is rebelling against what God has instituted, and those who do so will bring judgment on themselves" (Rom 13:1-2). So long as marijuana is illegal, it is wrong for us to break the law. We are called to obey the law when it does not contradict God's law. And there is nothing in the Bible that encourages the use of marijuana. So obey the law and quit smoking pot.

Also, it is unhealthy. Are you aware that 300 people die every year because of the use of marijuana?¹  Every year over 300,000 cases of hospital emergency visits are a result of smoking pot.² It is not as harmless as proponents claim. Plus it impairs judgment, and how could God want your judgment impaired?  

While God made the plant, it does not mean He meant it to be smoked or used recreationally. This is called abuse. The word "abuse" comes from the compilation of two English words: "Abnormal-Use". It's shorten by using only the first two letters of Abnormal, and thus we have the word "abuse". Abuse is when something is used abnormally. I believe the marijuana plant is abused.

You pointed out accurately that God made the green plants, and they are good. Of course you failed to point out that the green plants with seeds were given as "food", and that precludes using it other than for nourishment. (see Gen 1:29-31) Of course God made the marijuana plant, but He did not put a sign on it and say to "smoke it for recreational use." It is our job to find out the benefits of the plant. It is clear to me it is not meant for recreation. Some studies suggest that there may be medicinal benefits of marijuana. Now some use these preliminary findings as an excuse to smoke it. Rarely, if ever, are plants or trees used for smoking, but they often work better going through a medical lab in order to extract the beneficial aspects of the foliage. But doing this is not what the proponents of the legalization of marijuana want: they are simply looking for an excuse to smoke it for recreation.

Over all, unless you have an ethical, medical doctor's prescription for marijuana, I do not think you should smoke it. Do I think you will go to hell for smoking it? No, but I think it could hinder your positive testimony of a totally changed life. 

¹ http://medicalmarijuana.procon.org/view.resource.php?resourceID=000145

²  http://www.drugabuse.gov/publications/drugfacts/drug-related-hospital-emergency-room-visits