You should be extremely cautious when doing that. Delve into the law of your country and prepare. Many anti-money-laundering offices see bitcoin as an effective means of hiding and secretly transferring large amounts of illegally obtained value.

Who makes the decision of applying these new rules?

I would say, it will not become completely illegal and I also would not compare bitcoin to chemical or biological substances in the sense of criminalization.

Substances have direct effect on a person's biology, whether it is good or bad effect it does not matter, but it can make the argument emerge and thus justifications.

Bitcoin is a virtual object. It never has direct effect on people's biology. Also, it is unarguably evident that bitcoin is a more efficient means of transport for value. The only part that can build up an illegal aspect is that it can be used anonymously, thus also be used for money laundering and moving criminal money in large amounts.  Therefore the use of bitcoin might become strongly regulated, while it actually already is. All bitcoin traders need to follow the regulations set for a financial institution.

It is not only illegal, but it is a crime. Although the peculiarities of such a crime depend on the given law of the applicable territory, by principle in all (at least democratic) jurisdictions, refraining someone of the possession of his/her property is deemed to be a crime. The debate, whether bitcoin is money, commodity or something in between is not relevant here. The fact is that someone is its owner through regular means of obtaining such property, without damaging the position of others.

Criminal Law requires the existence of actus reus and mens rea in the case. What i have described was the actus reus, which is taking over the control of property without the will of its owner.

Now, mens rea means the mind of a criminal. That means that the person who perpetrated the actus reus was doing it willingly, presupposedly knowing about the consequences and presupposedly knowing that such an act was against the interests and the will of the owner of the property.

Therefore it does not matter how Bitcoin was taken from someone's wallet. Even if the private key was negligently on the owner's work desk, it is a crime using it for anyone else, without the permission of the owner.

There is a courtcase in Estonia, which has influence to all EU member states. It is Otto de Voogd vs RAB. In this decision bitcoin was deemed to be as an "Alternative means of payment" which means, it is handled pretty much as a normal currency from the anti money laundering and financial regulation perspective.

However, for tax it is different and really depends on each different state. Many states tax also assets which are not fiat, some don't. Estonian companies can keep every asset, including FIAT tax-free. In principle, bitcoin has a market value which corresponds to a fiat value, which means that no holder of bitcoin is relieved from tax, if there is any. HOWEVER, the other question is that how much the tax authorities can actually track and enforce the tax on bitcoin and playing around with this possibility is a risk in itself.

The only more super-governmental statement came in European Court of Justice Case C‑264/14 David Hedqvist vs Skatteverket, which set the standard in European Union that selling Bitcoins is exempt from VAT as being an alternative means of payment again.

Bitcoin is not necessarily illegal in Europe and being cooperative with the authorities right now is a way to sustain a healthy business on the area. That, at least, I can ascertain in Estonia.