I have only finished the first season so this may be answered differently in later seasons.
The moment Arnold realised Delores has achieved a sense of self and real consciousness he tried to get Ford to understand that these where not tools to be used for the entertainment of others. He understood that he needed to stop the park being used as a getaway for human entertainment because he understood the things that humans would do to the hosts.
That is made clear by a number of statements Ford says throughout the first season about Arnold. Throw away comments about how Arnold understood what humanity would do and he wanted the park shut because of that.
So Arnold realised he had to destroy the work and more importantly he realised that as his friend Ford would always be able to get him to rebuild and start over. He also lived with the guilt of his sons death. We can understand from how Bernard is programmed to make think about that event as Arnold did how Arnold must have felt and how it drove his work. It is possible that he didn’t trust himself not to start over in his lifetime and believed that whatever he did the same outcome would happen.
Arnold also seemed to understand that dying would risk the future of the park, Logan tells William, that one of the partners died, some hush hush thing that has opened an opportunity to invest and buy the park.
Ford himself tells Delores that Arnold almost succeeded it was only though the investment of Delos at the pushing of William that the park and hosts where saved.
But something Ford says to Bernard also makes me think that Arnold hoped that Delores killing him would do something else. Ford tells Bernard that he never saw Delores choice as free will because he convinced himself it was just Arnold making her do it.
So Arnold hoped that, in the end, by understanding what Delores did and why then it would prove to Ford that Arnold was right and so Ford would fab different path. A different route, maybe closing the park down or maybe doing something different with the hosts.