I think there are a few things going on here. I personally don't think a first birthday cake in and of itself is "trashy," or perhaps better described as trendy. Taking pictures of children messily enjoying cake on their first birthday is not a new thing. I do agree however, that those who do it (and feel the need to use the buzz word "smash cake" ugh) are probably more likely to blindly engage in the other trendy types of behaviors mentioned.
I am anti-bandwagon - not interested in the frosted professional pictures with color coordinating bunting and props, gender reveal parties, or any other type of thing that posters above have aptly named "trendy" or for "sheep." And I totally agree that it is a result of the "me, me, me" social media/mommy blog (omg those people need to go away) culture.
But, we did give our son his own mini cake at his first birthday party, which was just a small casual gathering of my family and my best friend at our house. I am a baking enthusiast and it was simply a matter of making one rectangular cake layer and cutting 2 circles for layers and then icing it. We got adorable pictures because (as someone stated above) it was his first real introduction to cake. He was extremely enthusiastic and we all took pictures and laughed a lot. It really felt like a celebration.
So I guess what I'm saying is that a "smash cake" does not always a sheep make, but a sheep will always have a smash cake
(As an aside, where are you people in my real life? I feel like I never meet anyone in real life who dislikes trends like this...)