Talmud Bavli Yoma 72b. How should be understood? The Torah was compared to a SAM mitah?
The Torah's words were called as a knowledge that can lead to afflictions? Shlomo Ha'Melech said "Derachecha darchey No'am ve'chol netivoteah Shalom(Mishlei 3:18,17,16)", and by the Navi "E'tz CHAIM hih Lamachazikim bah, vetomchea mehushar...(Yeshaia 42:41), and by David Ha'Melech: Torat H' temima MESHIVAT NOFESH...Pikudei H' yesharim, ME"SAMCHEI" LEV..., Mishpetei (Torah) H' EMET, tzadeku yachdab. Anechemadim mizahab (Tihilim 19).(Extracted from sidur Tehilat H'). Maybe rebbi Yehoshua was trying to convey what he thought (or his own expectations): what SHOULD DESERVE a person that do not study Torah in order to do the Will of H'. Rebbi Yehoshua expoused his own "din", on what this kind of person (with such intentions) would deserve?
The same with Reish Lakish. We are also told by Rebbi Yehudah that a person should always engage in Torah and Mitzvot even Lo Lishmah, for this will lead him to do them Lishmah.See Ta'anit 7.( I can't accept that RebbI Yehoshua called the Torah in such a derogatoy(despective) way: "sam mitah").Or maybe they said that because of the Kelalot?Tell me all... you can.
Have a nice day.
Tosfos explains (Berachos 17a) that not every Lo Lishmah is acceptable. If one studies in order to misuse the wisdom of the Torah for forbidden goals, it is better not to study at all!
As with any wonder-tool, the wisdom hidden in the Torah can be misused making it "poison" to those who misuse it. (An example in point is Alfred Nobel's amazingly helpful and amazingly destructive invention.)