Are dark thoughts, like racist, sexist, and anti-religious sentiments sent to the collective unconscious and do they become magnified there by joining similar thoughts to create an ever-increasing energy that echoes back to the sender to strengthen their prejudices?

This indeed is a powerful reinforcement and is in fact what happens. This serves to embolden people with the strength of opinion. Within their own mind, they are aided and abetted and all manner of distorted thinking by a similar distortion that affects the current culture and keeps alive disinformation, ignorance, and prejudices of all kinds. This reinforcement is a prime example of the power of consciousness to do evil indirectly, as well as directly. The stain of prejudice and bias thinking of all kinds is stored indefinitely and will serve as a beacon to guide many others on a false path. People have many teachers and as all are interconnected, this includes the worst among you as well as the best. One of the chief benefits of cultural progress is in the shifting of energies within the collective unconscious to “out shout” the misguided and evil notions that may be the norm for a while, but are gradually displaced by greater compassion and understanding and a willingness to be more forgiving and work for a greater good. And this changes the balance of energies within the collective unconscious accordingly and helps to elevate everyone. This again, is exploited through the shift in consciousness to maximize the exposure and the potential for implementing change through the influence of one another by amplifying the good within the collective unconscious to strengthen it, to focus it, and to help it run true, and give it greater power of intention to ensure it has an opportunity to visit like-minded individuals and reward their moments of clarity and positivity with a reward in the form of a “pat on the back” - a sense that they are on track and feel good about themselves. And it is the goodness coming from the collective that accomplishes this.