You don't have to. It speaks of your own independence

livedit:

Not necessarily.  IF, they speak, then of course, out of common courtesy, I would speak back.  But far as speaking to everyone he speaks too, it's not your duty too.  I would politely smile at them and THEN if they say, hello, how are you, then I would say it back. 

Just because you are a "couple" doesn't mean you have to lose yourself completely.  A smile should be sufficient and if you want to speak, then speak if not, then don't.  I love my husband to death, Lord knows I would do nearly anything for that man, but when we are out and he greet people and talking to them. I don't trip over my foot trying to run and greet them. Now if my husband introduces me or whomever he speaks with introduce themselves to me, then livedit greets back.  Other than that, a genuine pearle white smile is okay enough.

Perfect answer!

no it is not compulsory