Transphobic beliefs are, it appears, a primary variable that influences people to react aggressively towards transsexual women. However, there are many different variables where one's values and attitudes influences their behavior, which in turn results in some type of action being taken. Transsexual women are members of an esoteric social minority and we seem to violate some of the most cherished American traditional social norms. Aberrant social groups (e.g. transsexuals, lesbians, gay men, Muslims) tend to fall on the lower end of the class structure in our society because of their perceived deviant behaviors and attitudes that conflict with society's normative ideology. The laws of sociology show us how the variations in the patterns of social interaction between individuals, and or groups of individuals, will determine variations in people's behaviors and beliefs. This goes back to Durkheim's explanatory factor in social morphology, but I am not here to lecture on social theory. Meta-norms also play a huge role in the negative treatment of transsexual women. Group cohesion and social order are also thought to play a significant role on the willingness to impose negative sanctions on people who engage in behaviors which conflict with both in and outgroups.
For expository simplicity, transsexuality is generally seen as aberrant deviant behaviors which violate binary sex role expectations where transsexual women are viewed as an affront to masculinity and an assault on traditional social norms governing the appropriateness of human behavior. What further complicates this is that Transsexual women seem to have an attributional ambiguity that makes it difficult, and sometimes impossible, to determine if such negative treatment is due to some behavior or action on our part or because of our devalued group membership. How we are treated by other people has implications on how we view ourselves.
Once a person victimizes a transsexual woman they then try to rationalize why they did it but I believe they do it without any doubt initially in their minds, "Our logical inferences are mental habits; what we consider to be a valid belief is a habit of moving from one sign to another that is so well established that it takes place without any doubt at all" (Collins, 1994 p 251). Thus, a person's belief that the transsexual woman is disgusting seems to be so grievous an act; such a heinous violation of sex role expectations and social norms that the offender feels it is necessary to teach her a lesson whether it's psychically or socially (e.g. using male pronouns, being disparaging, arbitrarily increasing wait times, refusing to help, etc). This may be an automatic thought process caused by their long held belief system which in turn causes the offender to essentially loose control and lash out criminally. After the crime has been committed against the transsexual woman the offender, once arrested for the crime, may then try to rationalize why they did it. Here we can see that their reactions to being exposed to a transsexual woman may be an automatic response to that stimuli, but that does not justify or excuse beating, harassing or murdering her.
Reference
Collins, R. (1994). Four sociological traditions. New York, NY: Oxford University Press.