Just fighting fire with fire. If i am the host i either ask selected people before i send out invitations if they would take pictures, and at that point i make sure they get some kind of gift if they have agreed and are cool with it. it might be some cash, a gift card to restaurant they frequent, or it might be a bottle of wine. putting someone on the spot is just rude. i am that guy that has a basket at the door with envelopes and a sharpie so they can drop off their cell phones. the point of social gatherings is human interaction, not piddling with a computer.

As for parties i often wonder if the only reason i get invited to some is because i usually have a camera in the car. I don't start off carrying it in with me, but if anyone asks or if i see something going on and feel there is a need i will ask the host/hostess if they want me to go get it. Then I might record something like opening gifts or cutting the cake. If it is just a social gathering, most of the guests are there to blow off steam and a camera is regarded as an intrusion. If a challenge is issued between dueling idiots, sometimes that is worth recording just in case the insurance company or police need evidence. any activity that starts with the phrase "Hold muh' beer and watch this!" Is probably worth recording.