daf biyun, this method is often used by Frum Rabbis when paskening shailos. It would be shortsighted to state that it is purely a tactic of the Conservative movement.
Chas v’shalom. They don’t reject mitzvos.
I have a feeling you may be confusing understanding the reasoning behind specific halachos with understand ta’amei hamitzvos.
Perhaps you should give specific examples, so we can see what you’re referring to.