I firmly believe that the reason many Slytherins were easily convinced to join Voldemort was because they were treated like shit by the rest of the houses while they were growing up. Imagine spending seven of the most important years of your life being told that you were part of the bad house and therefore bad yourself. Everyone boos your quidditch team. All the houses will hang out with everyone except you. You grow up being hated by your fellow students and many of your teachers.
Now imagine someone comes along and tells you that you’re not worthless and bad. That you’re invited to join a family where you will right the wrongs committed against you. You have the opportunity to be wanted and powerful instead of a hated outcast. Several of your former classmates are telling you how great it is. How you’re welcomed and needed. These are the kids you grew up with. The classmates who went through all the same things you did. Being a Death Eater sounds pretty good now.