I use scrapbanking bots and I used to use key trade bots before that stopped being an issue for me (I have enough keys and metal now that I don't need to swap the two). I like trade bots. For standard trades, like currency exchanges, it's a lot easier to deal with them than with a person and, quite frankly, a 1-2 scrap profit for 2 trades doesn't seem like a worthwhile pursuit to me. I imagine that, without key trading bots, the key prices for selling and buying would be further apart.
As for autobump? Well, it's been my experience that most of the hate comes from one of two groups:
1. The entitled. These think that everyone else's time is worthless and those that list and babysit trades shouldn't get anything out of it other than a pat on the back for a job well done. They want to quicksell their items for full price and don't understand what's wrong with that. Either that or they benefit from sites like TF2OP, dispenser.tf, and DOTA2 Lounge and don't understand the concept of helping the site. Basically, they want all the services that the sites provide for free and don't see anything wrong with feeling like they deserve that, meanwhile expecting the people that own those sites to take all the cost (both in time and money) upon themselves with nothing in return.
2. The hopeless dreamers. These are the people that think that the reason why they can't get anyone to do a 1:1 Strange Ullapool (2,500 in the world) with their Strange PDA is because of the existence of TF2 currencies at all. Because, after all, currencies serve no real purpose in the real world and, clearly, everyone that wants to sell a Strange Ullapool would want a Strange PDA, right? If we just removed all types of currency trades and just traded items for items, their trade wouldn't be up more than an hour (if that). One day... one day.
Honestly, the most valid protest when it comes to autobump is that people leave it on when they sign off. This is (usually) a jerk move and I dealt with someone today that had their trades autobumping while they were offline for almost a full 24 hours, but I've accidentally done it and I do it intentionally when I'm (pretty sure that I'm) going to be offline for an hour or less. I also do it for my unusual trade and my dispenser.tf trade that I have posted on Outpost, since people shouldn't be adding me for either of those anyway. What I'd like to see Outpost do is default to not autobumping trades when the user is offline, which is what I thought was supposed to happen in the first place.