There is nothing illegitimate with the use of bots and many exchanges have the option to make it easier for you to communicate with their platform with a bot.

However there are many problems with the use of bots, as you may guess the first one is can the bot actually make profits in the market? And the only way to know that will be to know exactly what kind of strategy the bot is using and then test that strategy against past data but very few people do that and they begin to use the bot to trade not knowing about its capabilities, another problem are scams, people out there buy all kind of bots but those bots come not from companies with good reputation but from individuals that created their own software and that is a risk especially in this market because as we know once you lose your coins you'll never get them back.