I think there is supposed to be a nod towards individual rights (The Bill of Rights) and that a Conservative judge could rightly rule against a law passed by Congress that was Unconstitutional. But I'm not a lawyer. So let's say the Congress becomes a veto-proof Liberal majority and they pass a law banning gun ownership. Because they have a majority and they represent the people does this mean SCOTUS is bound to rule that it is in fact Constitutional?
No, the Court isn't bound to rule that a national gun ban is unconstitutional just because Congress has a majority and represents people. However, what the Court has done on abortion isn't comparable to a national gun ban.
A court is supposed to act according to the law as it's written, or to put it another way, the words in the written law matter. The further a court's ruling gets away from the actual words, the less legitimacy its ruling has, and eventually the court crosses the line from jurisprudence to tyranny and abuse of power.
There are actual words in the Constitution that prohibit a national gun ban. Where are the words that prohibit a state from outlawing abortion? The answer is that there aren't any. The Court got there by making some pretty big leaps from the actual words, which were, "nor shall any State deprive any person of life, liberty, or property, without due process of law." (See 14th Amendment.)
The first leap was that these words guarantee substantive (as opposed to procedural) rights at all, even though that's not only not included in the words, it's in conflict with them. Well, since we're now fully departed from the actual words, it wasn't that hard for the Court to make the next leap that one of those rights was a right to privacy, but that doesn't get us quite there either. The final leap was that abortion is implicit in privacy. Really? We're not talking about activities that take place in your own home. We're talking about a medical procedure that requires you to leave your home and seek the services of someone licensed by the state private. Even if we accept these goofy leaps and stop caring about written law, since when is a state prohibited from regulating the activities of people it licenses? It's absurd and illogical.
And to be clear, this is bigger than abortion. The doctrine used to strike down abortion laws is a catch-all doctrine that the Court has used to strike down pretty much any state law it doesn't like. There are no limits on that doctrine at all. It's arbitrary.
So yes, the court can strike down laws, but if we get that untethered from the words that are written in our laws, then what's the point of writing laws? We stop being a nation governed by laws and start being a nation governed by the whims and policy preferences of 9 people who account to no one. I'm not one of these hyperbolic, "sky-is-falling" people, but this is genuinely dangerous.