Are the movies in the series Back to the Future a disinformation campaign by suggesting that time travel cannot effectively change anything safely?

This is very much the case. The entire enterprise is to trivialize and minimize the importance of understanding and obtaining control over time travel. To be sure, there are pitfalls and many, many ethical considerations when undertaking such exploration, but this does not mean it is off limits. It is certainly not off limits to the interlopers who plague humanity. Their use of the time travel is a selfish and self-serving one. But that is like everything else they do, a function of their culture and spiritual disconnection. It could be quite the opposite and would be true for divine human with further growth and expansion.