I think it's up to the couple. If it's something the bride and groom have discussed before the wedding and both parties are OK with the Smash of Doom, that's one thing. I really don't have a problem with it, though I do find practice a bit silly.
However, more often than not, I have found that when one party smashes cake aggressively into the face of their new spouse, it's an expression of underlying hostility or an unconscious showing of where their priorities really are. A younger friend of mine made it clear to her fiance a few years ago that she didn’t want cake smashing, because she knew his friends were big fans of it and they would stand around the cake at every wedding reception they attended, demanding to see the groom smash the cake in his bride's face. Her husband to be didn't seem to take her very seriously, so she told him again that if he smashed the cake into her face she would see it as a sign that her newly minted husband didn’t value her feelings and wanted to see her humiliated in front of all their friends and family.
With his friends chanting, “smash it, smash it!” while the "happy" couple cut the cake, my friend’s new husband SLAMMED a chunk of cake into her face. I was seriously surprised he didn’t injure her neck, he used that much force. He didn't get any cake as she dropped his piece in the scuffle. She didn't say a word, just turned and went into the ladies room to clean off the icing and smeared into her face and hair. Her friends (myself included) quietly followed her to the ladies room to help her clean up, while her new husband and the groomsmen yelled after us to “learn to take a joke!” We practically had to wash her hair in the bathroom sink to get the icing and cake out, so her hair was a loss. And because there was icing in her cleavage, she changed into her going away dress half-way through the reception.
She walked out of the ladies room with her eyes dry and her expression blank. She wouldn't let the groom or his stupid friends see her cry, but she didn't tell them it was OK, either. The reception ended fairly quickly after that with the groomsmen griping about the bride ruining their fun. The couple did not have a good honeymoon.
The incident distinctly changed the way the bride saw her husband’s treatment of her. She used to shrug off the way he pandered to his friends, the way he told her to “lighten up” and criticized her for not getting jokes at her expense. She honestly thought she just needed to get used to his friends and their humor. Now, her eyes were open and she had a new perspective on her husband's behavior.
She divorced the guy within eight months. She gave him second and third chances, offered to go to counseling, but he didn't see anything wrong with his behavior and insisted she was the problem. She says if she gets re-married, she's only going to serve cookies at the reception.