While many individuals believe/opine that the major ...
This does not contain a complete thought.
While I agree that reduced biodiversity loss is a serious problem...
You probably mean that there are other pressing environmental concerns aside from biodiversity loss. If it is what you're trying to say, you have to write a sentence that states that point. Since this is a discussion essay, it would be better if you provide two reasons supporting your opinion.
... many people are of the opinion believe that ... species is the main a major environmental problem.
... in our life, as it provides our food and medicine, cleans our water, provides medicine for curing illness, and even creates ...
Moreover As a matter of fact, biodiversity is ...
If we reduce the amount of biodiversity declines, by driving many due to the rapid loss of species to extinction, we cannot expect ...
On the other hand, I side with those who ...
The two sides must be discussed in a balanced way in this type of essay. Do not directly say that you prefer this side. You only need to present a discussion about the other point.