The former Auckland and New Zealand University Students' Association president said that even as a public figure he struggled to be honest about his sexuality.
"If it's hard enough for me ... imagine how hard it would be for people in Asian or Pasifika communities, who are at real risk of being kicked out of home or being ostracised from their friends or family or church, simply for being honest about who they are and who they want to love."
Mr Do questioned whether the Asian organisations opposing the bill were speaking for everyone in the community.
"At least one thing that obviously unites the diverse Asian community is a desire to live free from discrimination, and to ensure everyone, regardless of their background, has the equal opportunity to succeed and live free lives."
Asian and Pacific churches have been particularly critical of Labour MP Louisa Wall's bill. Members of a Korean church travelled from Auckland to Parliament to protest at the first reading in August.
Public interest in the progress of the legislation has continued to build. The committee room was full yesterday, with observers forced to stand.
MPs expressed curiosity about a proposal to abolish the Marriage Act and replace it with a Relationships Act.
Submitter Graeme Pirie said this would further separate church and state. Instead of issuing marriage licences to celebrants, the state would directly issue a contract which recognised a couple's - gay, straight, or transgender - relationship. The couple could then choose to marry.
Committee members said it was an interesting idea, but would not resolve the argument that marriage was a union between a man and woman.