I notice not only coinbase but also others exchanges crashe when there is a big increase or decrease of bitcoin price. Maybe because of their hosting unable to control a lots of traffic during that incidents. So don't think coinbase has done this outages on purpose
Still, any exchange should never crash whenever there's an influx of users trying to trade on their platform. Being paranoid is not good but you should not trust them too much. We don't know what's happening under the hood after all. On top of that, it's perfectly understandable if people start throwing accusations when the same thing happened multiple times without any real fix (at least a fix people can enjoy).