When it comes to the superhero genre, legacy characters are somewhat controversial. The shoes they have to fill are almost always big, and when they've got a massive legacy to inherit, fan backlash is a foregone conclusion.
Whether it be through an unwillingness to accept change or old fashioned bigotry, some of Marvel and DC's finest characters have had to contend with their fair share of hate over the years. Even Dick Grayson, who took over as Batman in 2010, had to deal with an inordinate amount of hate, and he's been around since the forties!
The matter of legacy and who's genuinely fit to inherit it is a particularly salient feature of the DC Universe, where heroes have come and gone repeatedly over the years. Things are a little bit different at Marvel, where most characters have largely retained their identity over the past fifty or so years. That's made the matter a particularly contentious one for the House of Ideas, and while there are plenty of instances where heroes will never manage to win over certain fans, they can still prove them wrong by starring in a plethora of fantastic storylines - as has been the case in nearly every example.
Legacy heroes are here to stay. Best get behind them while you can.