The main argument against setting stops is that because you have declared where you want to be stopped out, your broker will move price to trigger your stop and they will pocket the proceeds.
There are obvious flaws in this whole scenario. But leaving these aside, let's suppose you use a mental stop to exit a trade which has unexpectedly turned against you. So right away, you're prepared to take two additional risks - one, that you will not see that price has moved against you and you will therefore not be able to manually exit, and you eventually get slaughtered when it turns out it wasn't just a pull-back: and two, that you will not be tempted to let price run a bit further against you as it might turn round, and a bit further because its momentum has now slowed down, and a bit further because you expect some good news.............. and so on.
Whereas, in a trend-following strategy, what's the harm in getting prematurely stopped out by a pull-back? So you bought in at 153.00 and you expect price to go to 160 for a profit of 7, but price falls back to 149 and you're stopped out for a loss of 4, which is annoying because the trend's still intact. So, is that the end of the game? No. You still expect price to go to 160 so you can now buy back in at 149, and exit at 160 for a profit of 11, less the 4 on the first trade, for a profit of 7. What's wrong with that?
Even better if you set your stop at 149 and your broker really does rig their quotes down to 149. They cannot keep their quotes adrift for long before they have to adjust back to the underlying, as not only you but all the other clients will be piling in with a target of 160. If you check the underlying when you are stopped at 149, and the underlying's at 150 and the trend's still intact with a target of 160, that's a clear buy signal and now the broker gets slaughtered because instead of you just getting 7 profit, you double up and buy back in at 149 but you also buy back in at 153 again. So now you have 18 profit, and it was the the broker who telegraphed you to do it. On top of which, they offered you a long position at 149 whose actual underlying price was 150. How long do you think they'd stay in business?