When giving an opinion towards something, it is ultimately personal. It has bias, and as much as you would like to make it factual, it is not. When going through things in life, viewing situations and living through them, it is hard to develop an unbiased opinion on a particular circumstance.
While watching the YouTube videos, I gathered that an opinion can never be proven to be true but a fact can be. That is what makes opinions, well, opinions, and facts, facts. An opinion may have supporting evidence because of the experience, but without solid proof there is no fact in opinion because it is a belief.
In terms of writing a thesis statement, to use an opinion would indefinitely weaken an argument because it is subjective and involves emotions and personal bias. Whereas using facts strengthens an argument because it is already proven true.