As you might know Stockholm is in a riot state currently where young criminals are setting fire to cars, shops and other things. They throw stones at the police, firemen and ambulance crews.
Mostly this is going on well out of town in suburbs where many inhabitants are immigrants with a high rate of unemployment and problems with lack of education. This might be similar to events a few years ago in Paris, France.
If you are in the city of Stockholm you would hardly notice any of this other than reading about it in the press. Can you visit Stockholm safely? Of course, Stockholm is still a very safe city. You might stay away from these suburbs at evenings and night just to make sure.
Sadly the young criminals only gain one thing from doing these things, most people in Sweden now grow a strong disrespect for them. Sweden have always been trying to help by giving people from unsafe areas around the world a safe place to live. You might expect people who get help to be grateful but in this case it seems that is not always the case.
It now seems that UK are warning tourists about visiting Stockholm and specially certain areas, https://www.gov.uk/foreign-travel-advice/sweden
For someone living in Stockholm it seems a bit over precocious but of course it’s better to be safe than sorry. However, not many tourists visits or would ever want to visit these areas anyway since there is not much fun going on, except burning cars and destroying others properties. Not normal tourist behavior.