Interesting question. Well, I will start by saying that I think the entire war on drugs is 100% IMMORAL. I believe any and all adults, aged 18 and older (maybe a bit younger like 16 for weed but 18 for other harder drugs) should be allowed to have any and all drugs they want for private use, so long as they are not operating heavy machinery or doing some kind of serious life-saving/threatening work while under the influence like being a surgeon, cop, working in the military, etc. The only other rules are that you should NEVER EVER be forcing anyone else to take anything they don't want, you should never mix anything with a drug you give someone as it should be pure, and if someone is mentally ill or impaired to the point that they may be unaware of what they are taking or doing even if over the age of 18, then that is a problem as well. Yes, an addict's family can suffer by proxy, but that's a different issue for a family to deal with on a personal level. A gambling addiction could do the same but we don't make that illegal...or well...we do, but we shouldn't...and also, no one pregnant should use drugs that could harm the fetus...
So that being said, because the war on drugs is IMO completely evil and immoral, does that equal the opposite, that dealing drugs is inherently moral??
I think you might be able to make a solid argument that it is moral. At the very least, because everyone should have access to what they want because everyone should have full bodily autonomy and choice over what they do with their own bodies and we are all denied that by the government, then in a way, those who defy the government and sell what we want are doing something that could be considered righteous and meeting a need we all rightfully deserve.
However, drug dealing as such with all the crime that can be associated with it can be very messy, so the issue isn't always that simple. If we all get what we want for a good price without anything ever being tainted, no one gets robbed or killed by gangs, no one drives under the influence, no one who sells the drugs uses that money to profit and then buy weapons and commit actual serious crimes, then the issue for morality in drug dealing is simpler.
But obviously if any of that bad shit is happening it's not moral.
So...if I were writing an essay supporting drug dealing as a moral activity I believe I could sell the argument, but only with the caveat that any immoral activities that happen through illicit drug dealing/or with the use of illicit drug money is actually the government's fault because they could regulate drugs and make sure they are sold without anything bad going down in the process.