I find that most games have a happy medium of having skill points in almost everything but diplomacy be almost worthless so you don't feel like you're punished for making your main character the party face. Clearly not a perfect system, and personally I'd rather have diplomacy checks tied to your reputation like Mass Effect 2 and 3 did it. It makes sense that people would be more likely to listen if you have a history of sticking to your word, or following through on your threats. Of course, that works for Shepard because everyone in the galaxy knows who they are. It's a bit harder to justify for your random nobody characters.