The city of Altanta has about 475,000 people (give or take). ITP (inside the perimeter, 285) has about 800,000 (give or take). The metro Atlanta area as a whole has 5.5 million.
There are a lot of moving parts here. Demographics playing a big part. Some areas are getting screwed. Grant Park is absolutely 1 of them. So I do feel bad for your friends. But the majority of Braves fans are in favor of this move - just the opposition is a very vocal minority.
They are vocal for 2 main reason in my opinion - and neither are rational.
1. It is a black eye for the city of Atlanta that they will no longer be in the city proper of Atlanta. but it is literally in a 10x better location than the current Turner which is south of Downtown and West of Grant Park literally in a wasteland of poverty. By being south of Atlanta, the core fan base (who overwhelmingly live north of Atlanta) had to deal with the connector (75/85 merge) which causes some of the worst traffic in the country.
2. it is moving to Cobb County. ITP'ers HATE Cobb County because it is conservative, somewhat anti-gay, religious, and has 1/2 the taxes of Atlanta and Fulton County. Some of the hate is legit in my opinion, some of it is crazy.
For the record, I lived in Inman Park for 5 years and Brookhaven for 1 year (both ITP) and now live in Smyrna about 2.5 miles from the new stadium. I wasn't really pro-smyrna move. But i was without a doubt pro-get the hell out of the current turner field area. It was a dump with NOTHING to do other than drink next to your car and try to avoid homeless people trying to sell you stuff or beg for money. It was not a nice place to bring out of town friends/family.