i would just like a pashut biur in rav eliezer's kal vechomer and rav yehoshua's pircha
hillel lowy, staten island, ny
The complete explanation of the Machlokes is dependent on the different ways the Machlokes is explained in the Gemara. However, on the simple level we may explain as follows:
Rebbi Eliezer holds that it is less of an Ones if the Korban a person was going to be Makriv had no way to be Karev b'Heter, and therefore he cannot be considered a To'eh b'Dvar Mitzvah.
Rebbi Yehoshua, on the other hand, holds that what makes the sin less of an Ones is when a person is trying to do something Asur (such as bringing a Pesach l'Shem Shelamim, since a Shelamim may not be brought on Shabbos), as opposed to when a person is trying to bring a Shelamim l'Shem Pesach, since his intention (offering a Pesach) is Mutar on Shabbos.