Eva X- I think we do actually understand what you mean. You want to know why we don't give advice when we comment to videos, and why we always tell the dancer that they are sexy, doing well, and such. Compared to some people (such as, in my opinion, Felix Cane) some people here may not be even CLOSE to that level of skill and beauty when it comes to movement, but that doesn't mean that we aren't doing well.
It's more about perspective on that- we're telling the person that they are doing well for where they are in the journey of dancing, and especially when we've seen their progress over time! Many of us struggle under the idea that we will NEVER be good enough, and that's our own opinion of ourselves. Other people may think that we are ALREADY "good enough," and it's nice to hear them say so!
For a lot of people, that little bit of advice can be devestating, and could possibly put their self-esteem and progress back by months, even years. It could be totally fine, like "Hey, I think you need to work on pointing your toes," but you don't know what that person is going through right now. They may have once had a great toe-point, but had a recent car accident, and had so much damage that they can't do it anymore. They are working hard at it, but from our perspective, it's not what we're used to looking at. Your comment could make them so self-conscious that they might give it all up completely! They might still be recovering from that accident, and you've just set them back, by that little comment.
A quote from you: "and believe me, if i'll post my videos i 'llwant to know what you REALLY think, not that i'n sexy when i don't etc.."
What if what we REALLY think is that you are sexy, and doing really well? What if that's all we can offer? Are you going to get fed up, and decide that everyone is hiding what they truly feel about your dancing?
As I said before, if you want the advice or constructive critisism, you can ask for it! And, please do! But most of us just aren't ready for that kind of scrutiny.