I don't want to sound too preachy but I find it often helps to assume the best of everyone. Most people aren't idiots, they just see things differently sometimes.

I thought about it a bit and I think that if you see something you disagree with or think is silly, usually that person either has different priorities to you (e.g. they might work in a document-centric company) or might just not have the same knowledge or experience. Either way, if you state your assumptions (in this case "relational data is important") and ask a question ("how does MongoDB handle this"), you should usually be able to trigger a respectful and productive discussion.

Of course sometimes there are just arseholes and trolls on the internet, in which case you can usually tell quickly and stop engaging.