It’s pretty much torture in many, MANY prison systems. Not to mention overused solitary confinement which is literal torture. So being tortured for your entire life instead of killed seems like a much harsher and inhumane punishment. Not to mention the guard abuse, abuse from others, etc…

These are not inherent to life with hard labor. "You shouldn't leave your house because you MIGHT get murdered" is not a sufficient argument against leaving your house. You can leave your house without getting murdered, therefore it is possible to separate the two, so attempts to avoid one should not require avoiding the other.

If your problem with life sentences is that sometimes people get tortured in various ways, then the logical solution is to simply get rid of the torture.

Now, if your actual issue is that you disagree with ANY kind of punishment, then that argument at least holds more water, since I can't definitively say that punishment actually works. It might, it might not, but if we assume that it does, then a life sentence has more logic behind it than a death sentence. And if we assume that it doesn't, then a death sentence is WAY worse.