I would argue that arguing over how big our websites are is not the important factor. I submit to you that PC electricity usage is the most relevant quantity we need to discuss when it comes to consumption of bits. I argue that the increased load on the network of sending more bits is negligible compared to the many endusers and their PCs that consume our data.
If we agree that PC electricity consumption is the most important thing to address, then we must ask whether or not the electricity generation process is bad for the environment. Most likely, electricity is generated by hydroelectric dams or coal/combustibles power plants. Suppose we replace those two types of power generation with low-maintenance, 50-year-lifetime solar panels (for which the tech exists). Can you still argue that the increased amount of bits sent over the wire for heavy modern websites is an environmental negative that we should address? I would say, no, at this point we have reduced the environmental impact of most electricity-consuming devices, and we can ignore PCs for the time being.
Therefore it is not the personal computer and the quantity of bits it consumes that should be your focus. It should be electricity generation.
I would like to ask you to consider whether or not your compassion-based arguments contain any resentment. Are you acting and speaking entirely on the grounds of compassion? And if so, how can you be sure that your supposed actions are going to reduce suffering of people and the planet and not have the opposite effect? How can you suggest solutions, like decreasing the weight of websites, and know with a high degree of certainty that it will produce the desired outcome (environmental preservation)? Could it have an unintended consequence?