I never said only teach in Tagalog, of course there are many words in many languages that have the same use where no other word will do, we see this in what we call 'tagalish' right? as well as words from other languages. In English we use a lot of French terms/words for things because of our close historical bond.
But the continued dilution of a native language will also, I think harm the culture as you become 'more' westernised.
Half of the magic of being in a relationship with somone from another country is because of the differences between you, I dont want my son to lose the 'magic' of being able to communicate with his elders who, maybe have not been as fortunate as him to be free to travel the world. Imagine him not being able to tell his grandmother about the places he has been or things he has seen. She speaks no English, so how else can he talk to her.
English has it's place of course and advances those who want to push forward, i have no problem with that.