He could lose the trust of the wizarding community. Harry is a symbol of hope in the regular story, and using dark rituals would shatter that image. This could lead to him being hunted or ostracized. Also, it might attract the attention of dark forces that he doesn't really want to be involved with. They could try to manipulate him further into the world of dark magic, thinking he's one of them. And his own magical abilities could be affected in unpredictable ways. Dark magic has a different nature compared to the light magic he's used to, and it might backfire on him.
One possible consequence could be his estrangement from his friends. In the original Harry Potter world, his friends are firmly on the side of good. If he starts using dark rituals, they might not be able to understand or accept his actions. Another consequence could be a corruption of his own soul, as dark magic is often depicted as having a corrupting influence in the series.
In fanfiction, if Harry Potter uses dark rituals, there are numerous consequences. Firstly, there's the internal struggle within himself. He has always been against dark magic, so using it would create a conflict between his old values and the new power he's dabbling in. This could lead to mental and emotional turmoil. Secondly, from an external perspective, the Ministry of Magic might consider him a threat and take action against him. Even if he's using the dark rituals for what he believes is a good cause, the Ministry may not see it that way. Additionally, he could end up setting a bad example for the younger generation of wizards, which would have far - reaching implications for the future of the wizarding world.
Chapter 404, "The Vice Dean of Hua Country Chinese Medicine University?!", is the clearest early answer because the rescue effort creates visible on-page results. It opens with Several minutes later, Jiang Li doubled back and knocked on Huo... and closes on So you're just an internet celebrity..
Chapter 719, "Borrowing Their Luck", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. Early on, Chang Rong: "Hmph, it has nothing to do with me anyway, since no one.... By the end, Xiao Xueyi looked at Su Yinwan's recent notifications in surprise,....
Chapter 860, "Is your friend feeling unwell?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, Beside him, Chang Song: "...." At least talk behind people's backs.. By the end, Beside them, Ji Yanbai couldn't help but marvel..
Chapter 815, "You've eaten through all the savings!", is the clearest early answer because it turns Jiang Bufan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Zhao Yuan was quite surprised, "Right, absolutely right, haha,...
Chapter 775, "Live Stream the Day After Tomorrow!", is the clearest early answer because it turns Chen Taifan's situation into a concrete plot event. It opens with After meeting Jiang Li, Jiang Shixu became much happier.
Chapter 784, "Slander Brother Yang Without Any Proof?!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on Could the person she saw right in front of her have been all an act?"...
Chapter 566, "New Game Begins!", is the clearest early answer because it turns Team's situation into a concrete plot event. It opens with How is that possible?" Luo Xuan frowned, "What's the rush? and closes on I have a bad feeling about this.] [Wake up, when King Zheng speaks,....
Chapter 538, "You Won't Get Angry No Matter What I Ask, Right?", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. It opens with Su Yinwan couldn't ignore Jiang Cheng's unusual behavior any longer...
Chapter 650, "Trouble on the Island?", is the clearest early answer because it turns Shang Shuyue's situation into a concrete plot event. Early on, Pei Ye instinctively shielded everyone behind him.. By the end, In no time, his body was marked with several scratches and bite marks..
Chapter 869, "This Marriage Must Not Happen!", is the clearest early answer because a shaky connection becomes usable in the plot.