Some who call themselves liberals have a knee-jerk negative reaction to anyone who professes support for the principles of Ayn Rand. They appear to do so based entirely upon the identity of the person, and not based upon any knowledge of the teachings of Rand. They mumble something about "Atlas Shrugged," throw in an ad hominem comment or two, feel smug, and move on.
Many arguments are available to oppose those who espouse Rand's views. Research what they are, and you will be in a better position to engage Rand proponents on a rational level.