The DDR had much greater problems after the war than West Germany. For starters most of the war reparations to Russia were paid by the DDR. The allies cancelled reparations pretty quickly after the war which was a massive fuck you to Russia as the total damage during WW2 to Russia was estimated at more than $100 billion dollars. Much heavy industry was stripped down and transported to Russia.

The fighting was also much more severe in the DDR. There was far greater reconstruction that had to take place to begin with as the east of the country was historically underdeveloped compared to west Germany.

These factors meant that the DDR couldn't compete with west Germany in areas such as wages and consumer goods. The wall was built and border controls strengthened because huge amounts of working age people were leaving the DDR for a "better life". The DDR had given them free education and then they were simply leaving and it was having a major effect on their ability to develop.

There were also much more practical reasons for closing the border. The Germany was the centre of the cold war. Why would you let spies and saboteurs into the country. (There was evidence of sabotage to key infrastructure).

I think the Berlin Wall was justifiable considering the context of the situation at the time. The DDR was not he'll on earth the country offered affordable living, good education and had very high living standards in general. It just couldn't compete with West Germany because of the multiple issues that the country faced.