Professor Carl Sagan was the Neil deGrasse Tyson of his day. So much, in fact, that Director Tyson studied under Carl Sagan and reproduced Sagan's iconic documentary series on advanced scientific concepts, "Cosmos'. One thing they also agreed on was the need to liberalize our archaic laws around Cannabis in the United States.
When asked about irrationality around drug policy in the United States he responded,
"All over the country we have people who have terminal cases of Cancer or Aids. Who are given for example huge doses of chemo therapeutic agents which force them to be nauseous, incapable to take in food. Which then leads rapidly to them dwindling away because they can't eat. It was been well established that marijuana counteracts this nausea and in the few cases where its permitted remarkable benefits accrue. Is it rational to forbid patients who are dying from taking marijuana as a palliative to permit them to gain body weight to get some food down. It seems madness to say we're worried that they're going to become addicted. No evidence whatever that it's an addictive drug but even if it were these people are dying what are we saving them from so that's an example of a highly irrational official government position on at least some parts of drugs we could argue you know case by case molecule by molecule but it means some parts of it are clearly irrational"
In addition, written in his seminal work Contact, the main character is out for a walk in Paris and walks by a store selling Cannabis imported from California. It is important to note that this has absolutely nothing to do with the plot, but that in the future he wanted to make clear a rational society would support full legalization. So at this point we are roughly a mere 20 years behind. We better get on it!
His most direct quote is probably,
"The illegality of cannabis is outrageous, an impediment to full utilization of a drug which helps produce the serenity and insight, sensitivity and fellowship so desperately needed in this increasingly mad and dangerous world."
― Carl Sagan
His protege also answered the question recently on his show Star Talk.
Let's be honest though, you don't have to be an Astro-physicist to support the Marijuana Justice Act, but you have to be a moron to oppose it.