Are males more likely to view homosexuals as mentally ill than females? It's generally accepted that males tend to have a more negative attitude toward homosexuality than females:

Three studies conducted with students at six different universities revealed a consistent tendency for heterosexual males to express more hostile attitudes than heterosexual females, especially toward gay men. (Herek 1998)
Men were more negative than women toward homosexual persons and homosexual behavior, but the sexes viewed gay civil rights similarly. Men's attitudes toward homosexual persons were particularly negative when the person being rated was a gay man or of unspecified sex. (Kite, Whitley Jr. 2009)

There's research into finding explanations as to why there is this distinction (e.g. Whitley Jr. 2001), but it does not seem to cover my specific question:
Q: Are heterosexual males more likely to view homosexuality as a mental illness (or  as some kind of a &quot;sickness&quot;) than heterosexual females?
The homophobia scales I've looked at (Szymanski and Chung 2008, Wright Jr., Adams, Bernat 1999, Raja, Stokes 1998, and Bouton et al. 1987) don't ask questions about whether or not homosexuality is considered a mental illness, but do ask if it's considered a &quot;sin&quot; or &quot;disgusting&quot;.
Craig Waldo (1999) is the only study I can find at the moment which sheds any light on the subject.


  Although negative social attitudes toward gay men and lesbians are often referred to as homophobia, several authors have argued that the term heterosexism is a more appropriate and inclusive concept (e.g., Herek, 1989; 1992; Lorde, 1984; Neisen, 1990). The distinction is an important one, as it focuses on the normalizing and privileging of heterosexuality (rather than merely a fear of homosexuality) and calls attention to the prejudice and social stigma, both institutional and interpersonal, faced by GLB people. In contrast to homophobia, heterosexism includes a wide range of experiences of discrimination not limited to those related to phobias or violent episodes, and it conceptually includes prejudice toward bisexual men and women as well.


As you said, men generally are less tolerant to those in the LGBTQIA community than women and Waldo suggests that it may be down to tolerance for hetrosexism.


  This study represents the first examination of a model of the process of heterosexism in the workplace, demonstrating that organizational factors such as tolerance for heterosexism contribute to its prevalence and that it is associated with undesirable job-related, health-related, and psychological sequelae. As such, this study provides insight into not only the costly effects that can be expected in workplaces that tolerate heterosexism, but also possible ways to counter it. By preventing heterosexism in the first place, both organizations and individuals alike will prosper.




References

Waldo, C. R., 1999. Working in a majority context: A structural model of heterosexism as minority stress in the workplace In: Journal of Counseling Psychology, Vol 46(2): pp 218-232.http://dx.doi.org/10.1037/0022-0167.46.2.218