I think we can bubble wrap stuff too much now days, the world can be a very cruel place so in my opinion it's best hardening up as early as possible so you are better able to deal with what it can throw at you.
I'm all about being honest with people, and don't believe in staying PC for criticism. But at the same time, being critical starts to tear people down. I don't think it does any good to tell someone who is fat "oh, you are just plush" or "oh, you are curvy and awesome". But heck, if they are strong, you do need to preface that by pointing out that they are not attractive. But jeez, they do need constant feedback that they are fat. I mean, at least your dad's criticism was targeted. It's not like you struggled with homework and he called you a chicken shit