That is something to consider. There is a difference though between working harder because you're afraid that you'll be replaced by someone faster and cheaper and working harder because you're motivated by feelings of guilt and shame. I don't think either one is particularly healthy, but in the former case you can at least make a rational decision whether the job is worth enough to you to risk burning yourself out.

It's also worth considering that not all developers are easy to replace, for various reasons. A lot of big companies aren't in a position to be choosy as long as their employees are reasonably competent and can do the work.