I work at a pet food store, so all my co-workers are into dogs to some degree. We all have similar feelings about nutrition (good brands, raw feeding, etc), and overall health/care, but we disagree about training methods and (occassionally) breeding practices/ethics. I don't want to start an argument at work, so I avoid those discussions.
I give customers at work honest advice (without downgrading any particular food or trainer or whatever) when they ask - but I don't give them unsolicited advice. For example, if a customer comes in with their unruly, ill-mannered dog, I'm not going to recommend training classes out of the blue. If that same customer comes in asking for training advice, though, I'll give them the bare minimum, and then recommend a class or private training, and give them some contact information - I am not a dog trainer, and I'll gladly leave that up to the professionals. Same with food. If someone comes in with their clearly unhealthy dog, covered with dandruff and smelly and all that, and brings Nutro up to the counter, I won't say anything. But if that same customer comes in and is like "I want to switch dog foods, my dog is itching all the time", then we'll have a conversation about it. I never, ever, ever say "Science Diet is a bad food. You should feed Orijen" - I normally go with the "Every dog is different, and not every dog does well on every food. It looks like your dog isn't doing well on Science Diet, let's try some other foods."
My classmates at school are all really into dogs and cats (obviously), but most aren't very knowledgeable about training or nutrition or behavior or anything. We'll talk about the cute thing our cats did the other day, or what kind of dogs we have, or stories about idiot clients, but I won't get into the other stuff.
My friends and family that aren't into dogs...well, we don't really talk about dogs that much. Unless they ask me a specific question, I just let it go. My friend was telling me that her boyfriend just got a doodle-thing from a breeder, and I just said "Oh, puppies are so much fun!" and we moved on. It's not worth fighting over.