why can't I uninstall Facebook, its very irritating!

why my samsung m21(4gb, UI 2.1) using lots of ram leaving nearly 1.5gb.

Why is facebook services preinstalled that keep running in background and why can't we uninstall this personal data stalking app.

Samsung Galaxy M21 has 48 megapixels camera, but the quality is blurry and poor like old 8 megapixels camera.

Network Connectivity after switching on/off Airplane mode, it stucks with no signal and after few seconds it shows edge connection, after waiting and changing network, 2g and 4g then it shows 4g volte!it's very irritating!