I think the bad feelings some people have about the phrase is because their parents used it instead of, not in addition to, an explanation.

When parents would lay out a rule, like look both ways before crossing the street, or don't touch the stove when it's turned on, and the kids would ask why, some parents' entire answer would be "because I said so" or "because I told you not to". And then they'd get angry with the kids for "questioning their authority", or because they believed the kids were asking questions for the purpose of being annoying.

Those attitudes used to be much more common, but I don't think it was due to the lack of internet. Parenting books and classes existed when I was born, and my parents still had this attitude. I think it comes from self-centeredness and a lack of empathy, personally.

I don't think the words themselves say anything negative about you as a parent, if you explain your expectations to your kids.