There are at least two things people debate regarding "Spanglish." The first is whether this linguistic practice is "acceptable." See Spanglish_Potowski.pdf for a few opinions on this topic, including mine.
The second thing people debate is whether the WORD "Spanglish" is the most appropirate term we should use to describe this linguistic practice. Is the term "Spanglish" a positive one, or does it reflect and create harmful connotations?
At the 22nd conference on Spanish in the United States (Feburary 2009, Coral Gables, FL), professors Ana Celia Zentella and Ricardo Otheguy were invited to publicly debate this topic. They generously agreed to allow filming of the debate. On this webpage you'll find a complete transcription in Spanish and a summary in English.