We had a big long thread about tyre stretching on another forum i use, with input from the law and manufactures, not only can it be considered dangerous due to the rim protuding but as tyres have recomended wheel width fitments and they are usually outside this on a stretched tyre they are considered to be illegal as the type approval no longer applies to them, thats a minimum of 3 points per tyres, plus any extra they want to give you for driving the vehicle in a dangerous condition.
Having said that lots of people get away with it, i reckon it looks stupid and like you couldnt aford the right wheel and tyre combination.