I'm going to echo your husbands sentiments here, a Sportster is a top heavy and quite powerful bike to learn on, if you start on a Rebel (or any similar smaller bike) you'll have to opportunity to learn much better bike handling skills than you would on a larger/heavier bike. I can't count the number of women I know who've given up on motorcycling because they started on a bigger bike and just "couldn't get the hang of it". Smaller used bikes tend to get sold from new rider to new rider so you don't really end up taking a bath on the purchase price.