Wise companies have no problem with people who join their program just for the promotions. In fact, they seek it. For example, if someone joins ABC loyalty program and accumulates a free night's stay worth of points, it encourages them to actually give that hotel chain a try.

For family, friends, and associates I assist (I do so because I'm good at it, and registering dozens of accounts for promos doesn't take much more time than registering one, if you automate a bit), I suggest that they sign up for every program under the sun. This way, when there is an easy and appealing offer, they know they can participate. As a result of this approach, my three young kids each have several free flights and hotel nights worth of miles/points, despite never having spent a penny to acquire them. Perhaps when they are older and they seek to utilize some of these freebies, it will turn them on to becoming regular customers of those programs.