I think the point is that there's a bait-and-switch going on: tell us a little about your ______ habits, and we'll give you this free stuff as a thank-you (and in hope you'll keep buying it. OK, no problem with that.
But after you've given the info, then it's 'oh you have to let us sell the data to get the stuff', and most of the time they don't just want to sell your anonymous little data points as part of an aggregated statistical picture, but your name and address as well as your customer data. It's not so different from giving out 'free' browser toolbars or smiley collections, except that in the fine print they also claim you've given permission for them to install a browsing monitor and what-all else.
And as regards baby products, they're taking advantage of the fact that new parents are usually exhausted and overwhelmed both practically and emotionally - not just for a first baby either, and this doesn't conflict with feeling happy. It's still stressful even if you're thrilled.
Carrying out a commercial transaction under the guise of friendly generosity at a time of unusual emotional upheaval is rather unethical. Consider too that not only do they want info about the parents; they're building a marketing profile on the kid that has just been (or even, is about to be) born, and realistically that data footprint is going to live longer than the actual person.
In find that creepy. YMMV, but even though I appreciate your point about it being a trade-off, it disturbs me that there's no easy route to finding who has your information and what they store. In many countries you can write and request that information of a company, but there's a lot of companies out there.