You will see, standing on your pedals has nothing to do with "being attached to your bike" - really. I know sometimes there are thing that somehow "feel" safer or easier in your mind without a reason, so you have a gut feeling that you would prefer to do it in a certain way.
Standing on your bike is quite similar to standing on a scooter, quite relaxed.

The idea of being clipped in on a mountain bike is horrifying me. I have a good friend who is going clipless on his MTB, and he is a good rider, much better than me. I think being clipped in helps him in certain situations like small jumps or going uphill over big roots.
That said, I had so many situations where I had to get my feet on the ground REALLY fast, or had to balance me by putting one foot on the ground, or even going over the handlebars very unexpectedly I cannot trust clipless pedals on uneven ground.
On the other hand, lifting your rear wheel with flat pedals or jumping is more learning effort at first than doing the same things clipped in. Being one with your bike certainly gives you more control.
And I have some "nice" tattoos on my calves from the pins on my platforms.