I didn't care for that particular dress either but I wouldn't go as far as to call it totally tasteless. It simply didn't appeal to me. Even more, I really didn't care for little Sasha dressed in black. It's such a harsh color for a little girl. She looked like Johnny Cash. Or Wednesday Addams.
And for the record, as much as I adored Jackie KO and her impeccable fashion sense, I didn't like EVERYTHING she wore either. The dress she married Onassis in, although a Valentino original was, IMO, childish and very inappropriate for a woman her age and stature, marrying for the second time. It was white lace with a high collar and puff sleeves, cut above the knee and then she had this big pollyanna-like ribbon clipped to the back of her head which looked ridiculous. I was only a kid back then but I remember being very disappointed by it. It looked as if she was trying to dress the part of a young ingenue. Not a sophisticated and worldly widow with two children. And it's funny. I spent almost half an hour just now looking for a shot of it and there aren't any on the web that show the dress in full. Oops. I'll bet I wasn't the only one who thought it was a dreadful choice.
But I forgave Jackie for that dress. Everyone commits a fashion faux pas at least once.