There are no incentives for doing that. If 98% of the network "discourages" a block, then those miners have a small chance of losing their blocks to the 2% that does not discourage the block. However, not discouraging a block has no penalty at all.
Excellent point. Although there should be a meta-incentive to make the bitcoin system successful, so there are lots of transactions (and lots of transaction fees for the miners). Certainly big payment clearing houses that want instant payments to work have the right incentives...