Why do people feel guilty to formula feed?

I have breastfed my baby exclusively for 2.5 weeks since his birth. It is too early for me to pump according to others although I have done it a few times b/c my breasts hurt so bad and my son wasn't ready to eat. So.. I have a wedding to go to this weekend and I will be gone the entire day. My husband's mother will be keeping the baby. I may not have enough milk saved up and pumped by this weekend as I can't produce that much and feed my son adequately in the next 2 days. So.. would it hurt to have formula available as a back up? Why is there such a stigma and should I feel guitly?? Eventually I will have to switch to formula anyway as I head back to work and have a strenuous schedule.