You always knew this was his dream. Your DH has made that clear to you from day one. So I can see why he feels the way he does.
However, when the visa process was started before, you didn't have kids. Having a child has made you want to stay close to family and friends at this current point in time, and that's also completely understandable.
For your DH, this move will provide him with an immediate community and focus through his work. For you, however, things will be harder. You won't be able to work for a while, and it will take you time to make friends and build a support network. Your DH does need to appreciate this.
That being said, moving with a child at this age is actually a really good time to move. You are still at the stage where you're attending classes and activities with your child, and so you'll meet other parents through those. There will be an expat community if you're moving to a reasonably sized city, and that will also be a source of friends.
As someone who has lived and worked in the US, I found it a fantastic experience. I missed home, of course, but learning to navigate life elsewhere and understand a different culture is hugely enriching and helped shape who I am as a person today. I wouldn't have missed the experience for the world.
I visit the US a lot as I have friends all over the country, and the scare stories in the media are not an accurate reflection of what everyday life is like for most Americans. Middle class people like you and your DH on the whole have a very good quality of life. Yes the cost of living has gone up enormously in recent years but that's the same here. I've just been over in the States for a few weeks and I didn't find the prices much different to the UK for everyday living costs. The US is a hugely diverse and stunningly beautiful country and living there for a while could be a truly fantastic experience.
That being said, it does depend on where you will be living as to the quality of life you would have. You need to know what city and what state. Some cities/states are more conservative, more religious and so on than others.Life in the Bible Belt could be very challenging socially for someone who is not Christian and not a Trump supporter, for example. I would also be very wary about living in a state with a very hot climate year round, or one with very long and cold winters, or one with lots of hurricanes/tornadoes etc. You also need to think about the cost of living in those places, the quality of schools and so on. This all varies hugely.
Moreover, you need to understand the package your DH will have and how far that will go in the area you would be living. Most importantly, you need to know what the health insurance will cover - this is such a major expense and with a child, you could be paying out thousands every month. What looks like a great deal/package on paper will be much reduced when you factor in health insurance payments. You also need to know what your legal status will be and exactly when you would be allowed to work. You and your DH need to sit down and go through all of this together and be realistic about what life this will offer for you both and your child beyond just his job.
Your DH needs to understand that this is not just about him. You need to be able to have a good quality of life and you also need to be able to work and continue your own career. Your child also needs to grow up in a place where you feel he will be safe and surrounded by people who share your values. Together as a family this needs to work for all of you.
Another poster suggested going on holiday to the area before committing, and I agree that is an excellent idea. I would also agree a mutual time frame for the move, if it goes ahead. Would you commit to say, four years, and then at that point, your DH would agree to come back if you want to?
You also need to be very clear on what would happen if you break up. If you have another child in the US and your children become US citizens, then you will not be able to take them back to the UK with you if you divorce and your DH wants to stay in the US. You may therefore be stuck there until your children are 18. It sounds like your DH is quite a self-centred person. If there is any chance you feel this marriage won't last, I would be very wary of going with a child to a country where my right to be there was solely tied to my husband's visa.
You need to have a lot of big conversations before you make any decisions. It could end up being a great adventure but it could also be the biggest mistake of your life. Either way, your DH will be fine - so you need to ensure you protect yourself.