Just because another player does not see the futility of a give position, that does not make it OK to ask them to give up. Some other games are actually enjoyable to get the final "kill", (even though Amazons isn't) so why not just offer a "GG" comment when the outcome is determined - maybe the other player will get the hint. Maybe their skills are so low, that they need to see the bitter end before they understand. Maybe they are just being difficult & it is the only satisfaction that they will get out of the game. Whatever the circumstances, it just seems rude to tell someone to give up (even a lost position)