That's more of a legislative thing. A legislature would answer the question of whether it should be legal, and the Congress has decided that it should not be legal.
The Court should decide whether the laws passed by that legislature are constiutional or not. Here, they have upheld those laws based on a broad interpretation of the commerce clause, which is one clause enabling an expansive Federal government. This is why the ruling is liberal, even if it doesn't produce a liberal outcome. Its the reasoning that matters, not the holding.
So... they upheld the ban on medical marijuana, and that was a liberal ruling.
When they removed the ban on abortion, that apparently was also a liberal ruling, even though it went against the expansion of government instead of towards it.
Here's a question: what court decision was not the fault of liberals? It seems to be the case that if a decision is p, then it is liberal, and if it is not p, then it is also liberal, which does not entirely leave a lot of decisions in the "not liberal" pile.
Its too different clauses of the Constitution. The marijuana case had to with Article I Section 8, or the Commerce Clause, and liberals have an expansive view of this clause. The abortion cases had to with the 14th Amendment, and indirectly had to with the 4th Amendment. Its not as simple as big or small government, powerful or weak government.
A liberal jurist would say that the govenrment, under Article I Section 8, that the government has the power to regulate interstate commerce. This would include regulating commerce where the transaction itself is not an interstate transaction (Like this case) or regulating things that aren't commerce at all on the grounds that they have an impact on interstate commerce, and to properly regulate actual interstate commerce, the powers of the government
mustextend to these other cases. So, a liberal jurist (Like Ginsberg, Souter, Breyer, and Stevens, the four most liberal judges on the court all of whom ruled to strike down the CA law) would say that allowing the state of CA to do what they're doing has an indirect effect on interstate commerce, and therefore falls under the Federal purview.
A conservative jurist would say that interstate commerce only means actual commerce that actually crosses state lines. As Justice Thomas said, if the government can regulate medical marijuana then their regulatory scope is hardly limited at all. It really has little to do with his view of medical marijuana and has much more to do with his view of the Commerce Clause.
On abortion, the both the liberal and the conservative jurist would say that the 14th Amendment protects three things: Life, liberty, and property. They also agree on what property means, more or less, and on what life means, more or less. The key difference is over liberty.
A conservative jurist would say liberty is the various rights and priviledges guaranteed by the explicit provisions of the Constitution and its Bill of Rights. For example, the First Amendment protects free speech, so free speech is a liberty that the 14th Amendment protects.
Side note- This is very important, because unless the 14th Amendment guarantees you something, the state governments can restrict it. Before the 14th was ratified in 1865, the states could regulate all sorts of things that the Bill of Rights protects. The First Amendment says "Congress shall make no law..." and it was actually understood to mean that only Congressional action was restricted by the First Amendment. So Alabama could ban the word "flower", and it wasn't a violation of free speech.
Back to topic- So a conservative believes that only those rights explicitly outlined by the Constitution are protected. A liberal jurist again takes a more expansive view. They would say that things like privacy are protected by the Constitution, even though not mentioned therin. The 9th Amendment says, "The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people." What rights are these that are not outlined, but still retained by the poeple? There are many approaches. International norms (If most countries don't have the death penalty, maybe we shouldn't either.), history and tradition (If the people have always been understood to have a certain right, they had ought to always retain that right.), and penumbras (If the specific rights of the citizens collectively seem to imply a right, then the people have that right. This is the key one in
Roe). In
Roe v. Wade, the Court held that things like the 4th Amendment protection against search and seizure implied a right of privacy from government intrusion. They used an expansive view of the Constitution to justify their ruling.
It is not as simple as one side always favoring big government and one side always favoring small government. Liberals believe in a big government on economics and a small government on social issues, conservatives want small on economics and big on social issues. But that's not even the best way to look at it, because your still focused on the holding (or the outcome) of the case, when you should be focused on the reasoning behind the holding. The best way to view judicial issues is that liberals take an expansive view of the Constitution, both the in powers granted to the government and in the rights retained by the people, while conservatives take a narrow view of the Constitution, whether considering the powers of the government or the rights retained by the people. Again, don't focus so much on whether abortion and marijuana are legal when deciding if a ruling is conservative or liberal. Focus on the reasoning.
A good parrallel to this case is
Wickard v. Filburn, a pro-New Deal ruling that had to do with the Constitutionality of the Agricultural Adjustment Act. The legality of agricultural production restrictions doesn't seem to have much to do with medical marijuana on the surface, but the logic behind both of these (liberal) rulings is essentially the same: That an indirect or substituted effect on interstate commerce justifies Federal regulation of something that does not seem to directly relate to interstate commerce.
I am also not "blaming" liberals for this ruling. I agree with the ruling wholeheartedly, and commend the court for sticking to its 200 years of precedent on commerce issues, so I'm not trying to blame those dirty hippies for taking people's weed away, I'm commending them for taking people's weed away.
