If Hamas hadn't been fighting around Al-Shifa hospital, it doesn't seem that there would have been an attack. Occupation, maybe, but Israel always had the option to turn it (or parts of it) into a crater, and didn't, even while fighting Hamas in the area.

So I don't think "Al-Shifa hospital is under attack" is suggestive that the speaker is thinking about the situation as opposed to reacting reflexively to rationalize their position. There are enough good reasons that one needn't reach for a bad reason like this unless one is rationalizing.

(Disagreeing with a rally's position on a ceasefire could be a totally sensible reason to not go to a rally, however. For instance, "Hamas needs to go AND an immediate ceasefire is needed because the current attempt to do it is killing too many civilians" would be a sensible anti-Hamas, pro-ceasefire position.)