It is different for simulated blurriness, because simulated blurriness can’t be modulated by your ocular muscles, so they won’t reflexively strain to focus.

You couldn’t really achieve that effect by actually putting any kind of lens in front of your eyes though. That is not a simulation of blurriness, it is actual blurriness.

The primary way it would be bad for your eyesight is by inducing eye strain, itself a primary cause of blurred vision. It’s a reflex of the subconscious brain - either your eyes will be constantly trying to focus, which strains them, or you’re consciously unfocusing them, which also strain them.

If you had eye strain causing blurry vision naturally and didn’t correct it with glasses, likely there’d be no downward spiral unless you have some other condition causing that. It’d potentially cause other issues like headaches or spasms though