He went to Alabama. Some people don't like him because of the college he played for. This is the dumbest of reasons to not like Ingram.
He "ended" the Bush era. Some people don't like him because after the Saints drafted Ingram, Bush wanted out. Bush was a fan favorite so no surprise some people are miffed about that.
He was overdrafted. Ingram is a talented player, but so far has not come close to equalling what the Saints gave up for him. When the Saints traded back into the first round to grab a player, people expected an impact player... not a short yardage back.
Mike Bell didn't get that kind of flack because he was a FA signed to specifically be a short yardage guy. There was no hype around him, everyone knew he was being brought in for one thing and that was to lower his head and grab 3 yards when the Saints need 2.