What are the disadvantages of kelp?

Could you kindly explain, in brief, what are the downsides of kelp consumption? Are there any particular health concerns that arise from eating kelp regularly? I'm also curious about any potential nutritional imbalances it might cause, or if it has any adverse effects on certain individuals, such as those with specific allergies or dietary restrictions. Could you also discuss any environmental concerns related to kelp harvesting, if any? I'm interested in understanding the full picture of kelp's disadvantages. Thank you for your time and insights.