Yes, to us, it's sort of like the child who cries when you change their diaper, or who doesn't want to take their life-saving asthma medicine. There is no choice. The poopy diaper MUST be changed, the child about to suffocate MUST take the asthma medicine. Period. *MY* child MUST rearface. As a parent, I walk a fine line...between respecting and nurturing my child's personality, and also protecting her and making important deciswiosn for her because she can not possibly understand the consequences. A forward facing 1 year old has a 500% greater chance of dying...we're talking brokwn neck, head seperating from spine, dead. My 15 month old has zero ability to comprehend that, so he gets no vote. Just like he gets no vote in whether or not to play in the street, poke shiny metal things in the electrical outlets, or any number of other activites with the potential to end in his death. It's my job to protect him and make those decisions for him, so that he *lives* to be old enough to make them for himself.
My kids can choose their clothes, their food, their daily play activities..they can not choose to put themselves in mortal danger. That's where I step in.
Yes,your child is at the age that they do sometimes throw tantrums in the car.
Pushing their feet against the seat is NOT dangerous. Now..if doing so causes the seat to move, or tip, etc,then your install is NOT good, and should be corrected immediately, preferably by a licensed tech. A properly installed seat is not going to move out of place even with a toddler pushing against the seatback with their feet.
Please try and find a tech on here in your area to help you, or else search for any tech in your area.