O.K.Sam2, I do not think they meant to do an aveirah. They had some heter in their minds.
HaLevi, you mixed up the Gemoras. There is a Gemorah that says about two people who volunteered to die to save Klal Yisroel that “no creature can approach their place”. It does not say it about the harugei Beitar.
Yichusdic, the mishnah talks about famous Tanach people.There could be others.
Coffee addict,Gemorah says he gets kaporah. I guess, issurim mechaprim. On the other hand, we say kaddish for him. It follows that not always such a person goes straight to Gan Eden. If he did not have the right kavonos, it for sure makes sense.