I'm brought up in an English speaking environment too. But no, I
dun fake my accent, nor do I look down on people who speak
mandarin. I switch (English/mandarin) when speaking with different
people, whichever makes them feel more comfortable, because Im
relatively comfortable with both.
I admit, initially I used to loathed the mandarin community of
Singapore. But that was in my secondary school days (I had a lot of
friends from ACS and other English speaking schools, resulting in
my relatively condescending attitude then). But now just a few
years later, I realized its what defines Singapore. Its what makes
Singapore so special. And slowly, I embraced people who for they
are, not by their language they speak nor the culture they were
brought up, but as human beings special in their own
right.