You get virtually no pH buffering from calcium carbonate sand either. Your pH would have to be pretty far out of whack for the sand to start dissolving and releasing carbonate ions at any appreciable rate. You can be thankful that that doesn't happen though since you would have to constantly replace your sandbed as it disappeared and your corals, snails, and LR would be constantly shrinking as well.
New quartz sand can release silicates for a while, and those can fuel diatom growth, but having high silicates won't fuel diatoms unless you also have high nitrate and phosphate to feed the algae. Some people actually dose silicates to promote sponge growth. Also, the initial release of silicates is due to contaminants in the sand, and after they are used up, the sand itself is chemically inert. It will not continue to release silicates forever.
The biggest concern is that if you get it caught between your magnet and the glass, you can scratch the glass, whereas aragonite is too soft to do that. The second biggest concern is that it has a translucent look to it in the tank that some people just don't like. If that doesn't bother you and you are careful not to scratch the glass, there is no real reason not to use quartz sand in a reef tank. It's not going to give you water quality problems or cut your sand sifters. Many people use it in reef tanks quite successfully.
