As mentioned, it shows a lack of control by the parents. There are certain cases, mostly around kids with special needs, where I am okay with it, but I see it as just another way for parents to be lazy.
If a parent is in a situation where they do not feel that the kid is safe, they should either pay attention to the kid or go somewhere the kid is safe. Providing a safe upbringing for a child, which includes the awareness to pay attention and/or paying for a sitter when you don't want to take the kid someplace is something I believe you sign up for when you have a baby. If you can't do that, if you are too self absorbed to get off your phone and pay attention to the kid, you shouldn't have a kid.