The issues I have with law/psychology/business studies at GCSE is that they are very much 'lite' overviews. They are not easy subjects, but they are not suitable for study at 14. These are huge areas - you aren't 'studying law' at GCSE, the best you're going to acheive is a basic understanding of the legal ststem and how it interacts with society. That ain't the same a studying law!
It would be very difficult to make those GCSEs harder because to study them properly at degree level requires the transferrable skills you require from other subjects and, in many cases, a mind free from preconceptions and simplifications. For example, at Chemistry GCSE there are 8 electrons in the shell and this is then readjusted at A-level when you find out that actually they're paired in subshells is only one example of how subjects become progressively more complex, and that simplfication at GCSE is not damaging to future understanding but simplifying, say, law could be infinitely more dangerous.
Teaching something in not enough depth or to people who lack the skills to process the subject in its entirety does more harm than good in the long run. If you have solid core skills, such as maths and English, there is no reason you shouldn't be able to follow a course in Business Studies later at more advanced level where you can explore complex concepts fully without having to learn how to write an argument, how to do basic statistics etc becuase you've learnt those transferrable skills from other subjects. If you have been drilled solidly in the basics (maths, english), your mind has been trained to approach evidence critically (science, humanity) and from multiple angles (english, science, humanity, MFL) and you are a confident communicator both orally and in writing (English, MFL, humanity) able to explain and justify processes (science, maths) in a reasoned way (science, maths) then there is no reason you shouldn't succeed.
I know some people will argue that some learning styles suit an integrated, contextualised approach better but that's why the skills are embedded in subjects and cross-curricular use of math, english and other key skills should be encouraged at all time. Geography, for example, requires decent English to write an answer more than 3 words long, arithmetic to analyse, say, population density and migration patterns, other mathematical skills such as the graphical representation of different quantities and interpreting bar charts, population pyramids and spheres of influence AND hones critical thinking and encourage a balanced examination of evidence. Yes, there's a certain amount of rote learning but memorisation and recalling appropriate information is a valuable skill too.
It's not that subjects themselves are easy, it's that we've been forced to make them easier to make them accessible for study at 14, which we shouldn't be doing.