To me it just feels wrong to incentivise living a certain lifestyle by getting a discount at just existing. It is great when it incentivises the things you want, such as hybrid cars or something, but what would happen if someone wanted to give you a discount for purchasing gas cars when they become less common because of relations to the oil and gas industry?
Or maybe tax incentives for purchasing private telecom service if/when municipal networks ever become commonplace?
If you they can lower tax liability for a certain amount why not lower it to the actual level needed across the board instead of keeping some cushion to give away coupons?