This is related to suggestion algorithms used by Netflix and other companies to whom accurate prediction of content that the users like is worth a lot of money. In 2009 Netflix gave a $1 million prize to a team who won their prediction algorithm competition:
https://en.wikipedia.org/wiki/Netflix_Prize

So if a bot is successfully voting for posts that the users enjoy, then it generates value. Steem is a complex system so it's difficult to say whether bots should be allowed or not. A serious problem would be if most of the upvotes come from shitty bots, resulting in noise.