How aggressively should we treat baby bottle tooth decay? My son’s dentist told me he has bad baby bottle tooth decay, and he wants to do surgery to fix it. Is this really necessary? He’s been eating and not acting like he’s in pain.

Yes. This is extremely important to treat before teeth abscess. Your baby won't loose most of their teeth until ages 8-12. It usually takes 1-2 years for a primary teeth to abscess. Fix this problem before it becomes more serious.
Very aggressively. This disease is emotionally and physically devastating. Very often by the time we see the child for the first time the front teeth are so destroyed that they need to be extracted. We can usually save the back teeth with stainless steel crowns. These children often dont complain of dental pain because they are so used to it that they think it is normal. Take this seriously.
How sad. Your child has a severe infection that can spread throughout the body. Don't wait...Have it fixed now before it becomes life threatening. It happens so fast in children. Get it tended today!
I . I am a pediatrician, not a dentist, but I have seen children with such bad tooth decay that is not only affecting their baby teeth but extending up to the permanent teeth. The american academy of pediatric dentists has a policy statement on the treatment of tooth decay here: http://www.Aapd.Org/media/policies_guidelines/g_cariesriskassessment.Pdf if you have concerns, you could always seek the recommendation of a second dentist. I would recommend a pediatric dentist though. Good luck!
Take this seriously! If left untreated baby bottle decay (also known as early childhood caries) will completely destroy a young childs teeth. Often they do not complain of dental pain because their teeth have been hurting for so long, from such a young age, that they don't realize it's not supossed to be that way. In addition to a having the decay treated you must improve this child's diet and oral hygeine habits.
It's a big deal. Aggressively modify the source of the decay (figure out when he's got sugar in his mouth and limit it to mealtime). Treatment options are highly case specific, and can't be determined without an exam; you may ask for a second opinion if you're unsure. Surprisingly, many dental conditions don't cause pain until it's long overdue, & bad things can happen if you postpone care.
Take Action Now!! Dental infections can become life threatening over night. Fast developing swelling in the lower jaw can obstruct the airway and localized infection can quickly spread to the blood stream. I can't add much more to this topic than the other qualified doctors on this site have already said. Please heed the warning of these professionals and proceed with immediate treatment. Don't wait!