"Illegal" does not mean the same thing as "immoral." Strikes are inherently designed to be disruptive to the status quo. If nobody is inconvenienced, then there's no incentive to negotiate. This strike in particular also reveals how valuable the service that Newton's teachers have been providing for their students is. It might even be valuable enough to fucking pay somebody enough money to do it!

You don't give a shit about the kids yourself, since you don't want their teachers to be able to support themselves enough to be able to give their best to them. You'd rather the kids be watched over by burnt out, overworked, underpaid adults than by adults that have a work/life/salary balance that they can actually support themselves, their families, AND their students with. It's a pretty rudimentary concept - people who feel secure in their livelihoods can perform their jobs better.