I don't think your fictional Newton is really invoking the anthropic principle.

In all the zillions of galaxies that exist, the ones where intelligent life developed are more likely to be observed by intelligent life. Therefore, intelligent life can't make any arguments based on probability that intelligent life developed, because our observation of the phenomenon is not independent.

And maybe some people have used it to avoid explanation, but it also doesn't really conflict with any effort to explain either.

more likely or less likely has nothing to do with observation indipendece. I flip a weighted coin and it's tails 99% of the time, it's the coin that is weighted it has nothing to do with me. The same thing with the parameters of the universe, the fact that life is present on Earth and not on Mercury (to take an exterme example) is not dependent on the observer being intelligent or even alive. even a non intelligent "aparatus" can detect it. it may not "know" to clasify it as life/not life but it can detect the difference.

Saying that we wouldn't be here to ask the question is not an answer to anything because we are here and we need to understand how and why.