Yes, unless they have committed a crime

Just as language is part of our identity, citizenship also gives us a sense of identity. Unless a crime has been committed, a government should have no right or reason to deny someone dual citizenship and is even considered unjust. There’s a great article here on dual citizenship in ‘Dual citizenship as human right’ by Peter J. Spiro (https://academic.oup.com/icon/article/8/1/111/682643?login=false); see paragraph two, following Abstract.