Why is using drugs a sin?

The political far right, big pharma,and the televangelists know that people would be generally happier and less receptive to their propaganda if products containing thc were legal, hence it is not and were are so numb we tolerate this. They hate they sound of laughter and joy.

You have the answer already.

There is nothing from outside a man entering into him which can defile him; but the things which go out from him, those it is which defile the man. - Mark 7:15

it is not what goes into the mouth that defiles a person, but what comes out of the mouth; this defiles a person. - Matthew 15:11

It's not the use of the drug that makes it a sin, but the result of using the drug that makes it a sin.

For example, drinking wine is not a sin (it was also a common practice during Jesus time) but drinking to become drunk is. Bottom line is, God hate people who tried to achieve personal satisfaction outside of the Lord's way (like saying God's is not enough for me so I'm going to find my own satisfaction another way).

Genesis 1:11-12 isn't talking about weed. There's more herbs than that.

Mark 7:15 is about evil in the heart. There are verses that forbid getting drunk, which could also be understood as not getting blown.

Matthew 15:11 again is about evil in the heart.

"So where does it say that drugs is a sin? If you quote "respect" the laws of the land verse, then if hypothetically; they legalized drugs and outlawed churches and praying, would you abide by the rules of the land?" No. That wouldn't be just. And we're supposed to put God above all else, even human authority. I wouldn't stand for a wicked, tyrannical government.

I don't need that stuff... It just hits me hard in the long run.

Paul never contradicts Jesus

Jesus drank wine, or maybe made it and exceeded it out to others. Does that sound like a sin? It relies upon on who you ask. There are all forms of religious nut situations who will inform you that each little thing is a sin. in case you abuse drugs then maximum folk might agree that it is unwise, if not a sin. If everyone tells you that taking a drugs prescribed with the aid of a doctor is a sin then they seem to be a nut case for effective.

It's not just about obeying laws but respecting our bodies. Drugs aren't natural for us to take so that we hallucinate or get high. This is God's view on harming our bodies:

(2 Corinthians 7:1) . . .Therefore, since we have these promises, beloved ones, let us cleanse ourselves of every defilement of flesh and spirit, perfecting holiness in God’s fear.

God promises us that he will give us everlasting life without pain, suffering or sicknesses. As a former drug user, I can say that most users do it to escape this life. You quoted from Genesis 1, Chapter 2 goes on to say that Adam and Eve lived in paradise, in Eden. Their lives were supposed to be full of happiness. There was no need for escapism. When God finally brings about his purpose that he had for Adam and Eve, we will see that it was worth keeping our bodies and spirituality clean.

Some feel that one reason is that one of the greatest gifts from God is our free will. This means we can choose to follow God, or not to follow God. Anything that is addictive limits our free will in that you may become addicted, and no longer have the ability to exercise your free will (as the addiction has taken over and pretty much mandates you follow it). I know not all faiths believe in free will, but for those that do, this explanation may work.

There are no sins. A sin is just a rule or law religious folks live by, forget their rules and laws and do what you want. Some drugs are against a different type of law so you have to be careful there but forget the jesus is watching sinning crap.

Who is claiming that it is a sin?

Like you say, drugs in their natural form are plants, given to mankind by God for our benefit.

But humans have a knack of taking good things and using them in excess. I think most people would agree that it is a good idea for society to discourage people to get addicted to heroin for example. Bad outcomes all round.

More people are in prisons because of what they did while on drugs than for any other reason. Drugs allow the demonic realm to affect what you do and how you act. The spirit of pharmacea is a dangerous spirit than can destroy a person's life. Only faith in Jesus Christ and the blood he shed for our sins can help people overcome such addictions and demonic powers.

Drugs are bad for you, so since it is bad for your health and if you use too much it can harm your body then God doesn't want that to happen to you.