Funny thing is, they do help you. Sure, there's assholes who see a signal as a sign that they need to speed up to prevent a lane change, but there are plenty of people who will see the signal and let you in, at least in my area. My own rule of thumb is if I don't have to slam on my brakes to let you in, I'll slow down for you, especially if you're a semi.

Unless I know you pulled into an onramp lane just to skip ahead of the people not doing that bullshit when it's stop and go level traffic. But it's usually hard or impossible to tell who is an asshole and who is just using the onramp because they just got on the highway and I try to leave space for people just getting on.