I think Thanos had the right motives and goal (in the movies - I havnt read any comics) but his plan to get there wasn’t great. Even assuming removing half of the consuming population is the best solution available (if you can completely alter all of reality why not just make more or infinite resources?), his plan to just randomly select half the population, delete them, and leave them in their loved ones memories is overtly torturous and malicious to everyone in society. He could have taken more care in the selection process instead of just taking at random, or he could have altered people’s memories so they didn’t feel the loss.