Well, I guess there's something to say either way. What I find more silly, but which I see in many games, is first getting the choice to either creampie or not, and then the partner (so not the MC) making a request according to that choice. Also, I'd rather see the wishes regarding this discussed before doing the deed, instead of during it. It's not always suitable to the story to ask in advance, but if the opportunity is there, I think it's pretty normal to agree on the groundrules before committing.
Always doing creampies doesn't make too much sense, there's too much to consider, from pregnancy to STDs. But auto pull-out isn't always logical either, and some people are just not fond of it, so it might be good (for future games) to give some explanation to why an MC either auto-creampies or auto-pulls-out.
Whether the girls would even get pregnant, yeah, it depends on a lot of things, and is often similar to a lottery. And for all we know, the girls developed some means for anticonception in their own world? But earth birthcontrol may be an interesting subject to educate the girls about and become some side plot on its own.
