译成背弃自然不妥。give up是最好的解释。背弃有放弃，背叛，反对之意。入籍誓词只是要宣誓人自愿放弃对原籍国义务，并没有要人家背叛。
1.     to give up or put aside voluntarily: to renounce worldly pleasures.
2.     to give up by formal declaration: to renounce a claim.
3.     to repudiate; disown: to renounce one's son.