Should I share my course notes with my co-students?

You have just discovered some of the seemingly irrational ways in which students sabotage themselves and behave contrary to their own interests, and how they sometimes do this precisely in response to an attempt to help them by offering them useful resources.

Professors constantly struggle with this issue: do I offer my students lecture notes? A practice exam? Homework solutions? A detailed outline of the topics I covered in each lecture with precise references to the textbook? Etc. What one observes is that sometimes by the very act of offering such resources you paradoxically hurt the students by reducing their incentive to come to class or take other action that is important for their educational success.

What makes these decisions especially tricky is that almost always, offering these resources does in fact help many students while at he same time hurting others who have the inclination to respond in this counterintuitive and self-defeating way. So it is a real dilemma about whether you insist on helping the "deserving" students who are not tempted to slack off because you made their lives a bit easier, or take a more "social engineering" approach that tries to optimize the success of the class as a whole without getting drawn into moralistic judgments about which students' needs are more deserving of being addressed.

To summarize, I don't have a good answer to your question. All I can say is that you need to think what goal exactly you are trying to achieve by sharing your notes, and then consider (keeping in mind my analysis above) whether the sharing actually helps or hinders that goal.

Your main concern appears to be the pedagogical aspect of posting your notes so widely. Is it your responsibility to worry about whether it is doing your co-students a disservice? @DanRomik is pretty articulate in his answer about faculty struggling with this same question in all aspects of course design and administration.

You are a student, the more relevant concern should be; Is posting the lecture and class notes as you do supporting the faculty's methods for the course design or not. Are you are working with him or counter to him? (This is only coming up in my mind because it sounds as if you have a rather large operation going that large numbers of students are counting on! and is affecting how they interact with the course/professor).

If I were your professor, I'd prefer if you eventually came by to ask me whether I found it helpful or not. I'd likely welcome that the notes are posted. I may have some requests to tweak the timing or type of information you post because of other administrative bits that you don't know. Or I may tweak what I do in class to use it to better advantage for all students.