It's bad practice and here's why. There are a finite number of smart people on the internet, and an even smaller number that want to join your community. The top 1% of users really determine the quality of the community. If you lose 1 one intelligent person ready to make a large contribution to your forum by banning Indian IPs you have hurt your forum immensely. Ban people on a case by case for terrible English/stupidity. Sure it takes a little more time, but it will be worth it.
I agree with you in principle, but for this community I need people who can write proper English more than I need highly intelligent people. And out of the 30 random users I checked today from India, not 1 wrote posts or comments in what I would consider to be acceptable English for a "professional" forum.