You see, mushrooms have a will of their own. LSD doesn't, it's just a raw force that needs to be harnessed and steered to the right direction. Now, if you care for the mushrooms, cultivate them, treat them with love, they will also treat you well and care for you during your trip.
Then again, some people may feel intimidated by the strong presence of another awareness with a direct connection to your mind, when they trip on shrooms. Maybe they don't know the mushroom entities well, and the mushrooms don't know them, so they feel strange to each other. So they feel more comfortable with LSD, where you have to steer the trip yourself.
And the people like me who are very familiar with the mushroom entities, find that they take care of them during the trip, and they can just let go and let the mushrooms steer their trip in the right direction. And on acid they feel threatened, since the familiar presence is not there, and they are not used to having to control the trip theirselves.