If people have the choice then it negates some of the benefits:
"Dear possible spammer / scammer - we provide a way to protect against your subterfuges from being found out by hiding the fact that you are posting through anonymizing proxies. Would you like to use this feature?"
... is effectively what it says.
If you are so concerned about your identity then why do you surf the web directly from your own location? Why should this site assist you in possibly promoting a false persona?
Have you ever asked anyone where they are from but been dishonest about where you are from?
If you want to be anonymous on the internet then it's up to you to make sue you are anonymous. Yes, others may chose to limit what they share with you as a result because I think that they have a right to know and limit how much they share with someone who choses not to share things with them.
It's not like we're dealing with the CIA or ISIS. There is no hit squad constantly on the lookout to track people down. They are JWs ... they don't even know what is going on in the local KH's most of the time.
Can you understand why I am skeptical that a country alone from what will inevitably be one from a list of 3 or 4 for +95% of posters would possibly identify you?
If you think your posts + country already identify you then you are already identifiable because I can say "hey, what if they are from the US ... or the UK ... or ...". Within 3 or 4 countries I've covered most bases.