First of all, you have to know a reason based on common sense that What Islam told us to leave, we have to leave it. Where Allah and Prophet Muhammad put Full stop, we should not go even an inch beyond it.
About your point of weed, Heroine has somewhat same effects on people, but can we make it legal?
In short, what is Haram in Islam, no matter how many benefits it has, we have to consider it Haram and avoid it at all costs..
Anything that causes intoxication is prohibited in Islam according to our beloved Prophet Muhammad peace be upon him:
Narrated Jabir ibn Abdullah: "The Prophet (peace_be_upon_him) said: If
a large amount of anything causes intoxication, a small amount of it
is prohibited. (Translation of Sunan Abu-Dawud, Drinks (Kitab
Al-Ashribah), Book 26, Number 3673)"
"That which intoxicates in large quantities is prohibited in small
quantities." (Abu Dawud, Tirmidhi, Ibn Majah, and others, with a sound
chain of narrators)
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