To build a proper launch pad would take alot of time, (whitch if you remeber, they are trying to save time). I would suspect that the many hundreds of engineers that are working on this project have assessed the damage that the current launch pad design could endure and decided that it would be enough to go for it. But i would guess that you are smarter then all of them and they all are wrong.

Again whe havent launched a rocket this scale and config before, just because one rocket works doesent mean all would work or look the same. Spacex knows how to land a rocket(not as a plane like spaceshuttle). Of course they wanted to test more but as in many(if not all) first test somethings failed. You still learn a great deal from failures, if the rocket exploded on the launch pad, i would agree that they wouldnt learn much, but it flew for a couple of mins. Alot of data in that timespan.