Honestly, I voted no mob greifing. I never have problems with creepers, it's very rare to lose anything above stone or a chest (with the items just ouutside), but, we've all had that one fluke. Maybe your fluke lost you two diamonds, but someone else's fluke could potentially make them lose a double enchanted thaumium uncrafted diamond pickaxe that cost them 80 levels to create, or maybe the aqueous accumulators below their huge boiler could just break, and when they try to add more? BOOM. Maybe an advanced solar they were going to add to their array was during nightime, and a creeper spawned up there. That could be lots of their precious (expensive) solars. Maybe you're electrolyzing some sand, and a creeper comes along and knocks your electrolyzer into a machine block, which, unfortunately, was wired into all your other machines, poof.
Do you really want creeper explosions? If you have never gotten blown up by a creeper, count yourself lucky. They'll remove items, maybe you kept your diamond chest to hold items, that could very well be gone (not to mention the enormous amounts of lag one could get when they break a diamond chest full of stacks of cobblestone--or anything rarer). If you really want creeper explosions on, make a pseudo one. Go remove 5-10 blocks around the epicenter and pillar up 10 blocks with some sand and jump off it. Congratulations.
But I'd like to hear some reasons why people want it enabled. For the "play legit" argument, I could say that it's FTB, triple ores aren't "legit".
Personally, the creeper explosions aren't much more than a minor inconvenience (gotta smelt that cobble, gotta smelt that glass, gotta make a new crafting table), but, to some people, creeper explosions will take chunks out of their boilers. My base is well lit, but everything spawns in it, though rarely....why? Good question >.>