1) yeah, security is an issue, but I am not convinced that you can't have both secure online plus unsecure offline.
2) I'd play D3 offline or with family anyway. I'm pretty sure I am far from alone on this. I'd wageroffline/lan is far more frequent than online play was, on a per unit sold basis rather than per hour played (better replay value online)
3) I bought GW1 for multiplayer option, as in optional. I've done lots of PUGging and ally events when I felt like it, and I enjoy trading.