Your comparison is exaggerated. Two crashes of the same model and similar circumstances in less than 5 months, for a model that's under 2 years old and only 350 built in total raises suspicions. It's not a good record. The very fact that the suspicion exists is enough to back up the reasonable claim. Whatever the problem is (design, pilot training, etc.) it's hurting this model and its passengers so it should be investigated without risking more lives. Precautions are always based on suspicions. Otherwise they're no longer a precaution.

With aviation experts, governments, and even airlines (bearing the costs) agreeing with the grounding measure I think I'm not too far off. The list in the article above just gets bigger. The current situation lends a lot of credibility to the idea that the plane might be to blame. Grounding them could be expensive. Not grounding them could be criminal. Which one would you choose if you had to?

Also this: https://news.ycombinator.com/item?id=19369485