Are some fantasies evil? If you have a fantasy about killing your boss, is that evil? Isn't that like saying thoughts can be crimes? Are thoughts capable of being immoral, without ever having been acted upon?
Biblical ethics of course condemned sinful thoughts. There was the double-whammy of such defiling the person entertaining them, even if the imaginations did not incubate the eventual urge to act upon them.
The Orwellian definition of thoughtcrime seems to have embraced even the "unspoken" state of holding illicit beliefs or doubts about IngSoc ideology and its standards for behavior. However, if no action ever made them publicly perceivable, then there was also no brain-reading technology to discern the mental violations. But the movements, reflexes, facial expressions, and overall body reactions of inner-party members were constantly measured by the monitoring system of the Ministry of Love for hints of improper thinking.
Aside from the assumed inherent properties itself of an "English Socialism", supernatural theism would have been rejected since the claimed help of an omnipresent deity -- which could privately access the introspections of humans -- would be a rival to devotion and affection for the State as god. For the same reason sexual interaction, family, and love were temporary "necessary evils" which would be expunged in the future by scientific research. In the end, "crimestop" conditioning was the replacement for religious or traditional social-based guilt, when it came to individuals personally aborting their own illegal mental activity.
Today (or in this actual world), morally and ideologically incorrect fictional thoughts that remain completely hidden seem secure from judgement by agencies born from "terrorist paranoia" and the gradually emerging "daycare authoritarianism"[1] of the Millennial Generation. The latter being currently confined to college campuses (where students have more intimidation power). But the ubiquitous presence of cameras and smartphones provides the potential for similar degree of scrutiny as
1984, and it's really quite impossible to hoard private thoughts 100% of the time without what is written, said, done, or stored revealing or misinterpreting something via a bit of nosey inference applied.
What about sexual fantasies? If you have a sex fantasy about rape but never act on it, does that mean you are a rapist? How can it be, given that rape is defined as nonconsensual sex with another person?
It might carry weight in the context of dreams, at least. They often feature external-worlds populated by communities of humans with varying systems of moral prescription. Their own judgements about the dreamer's avatar committing a sex-crime against one or more of their virtual denizens spurs their virtual manner of punishment becoming applicable. Although in waking state it would all be deemed an imaginary product of neural processes, the avatar's commonplace amnesia in regard to its "transcendent identity and life" (when total) would render it believing the simulated events to be real at the time. In turn, this would mean the avatar performing crimes which it believed were actual (thus the responsibility factor). The dreamer, however, can always disassociate itself from the avatar's actions upon waking via one or another argument, especially if it was a vicarious dream of being someone else entirely.
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[1] Which is to say, a form of extreme nanny-state where adults are to be protected as if children from exposure to incorrect speech, attitudes, materials, covert or micro-aggressive humor, and anything potentially breeding a tendency toward offensive behavior of any degree.