From the point of view of the original angel investors and early employees, why shouldn't the founder push for the best, least dilutive, offer? Are you suggesting that if VC2 comes in with a low-ball offer, the founder should just say "gee, they made such an effort, I owe them the right to excessively dilute us all, even though VC1 is putting his money where his mouth is, and is willing to step up to avoid it."
Let's say I helped you by putting up a down payment for you to buy your house, for which I get 10% ownership. Later, you want to sell the house (or a further interest in it). If you get an offer, and I think it's too low, is it unreasonable for me to want to "steal the deal" at that artificially low price? Otherwise, it's simply a transfer of wealth from me (and you) to the new buyer, which I'd certainly like to defend myself against. People buy houses all the time in competition with other buyers; no serious buyer says "I'm not going to make an offer on that house, because someone else might beat my offer, or maybe exactly match it and the seller could choose that other offer."
