I don't think it's really the "rescued by a man" thing - although I'm sure that bothers some people. Personally I thought she did most of the saving as all the male Avengers seem to run out of ideas after "HIT STUFF". And yet the thing that appears to affect her most (in the film) is that she can't have children - that seems utterly out of odds with the character and unnecessary to the film.
I dunno, I think so much has been made of that small scene, yet no one seems to be taking it in context.
Banner says there's no future with him because he's a monster and can't have kids, he can't have a family and a normal life. She says she's a monster too, that she's done terrible things that she's making up for, that at the end of her training, they sterilized her so she could never have kids, never have second thoughts or compassion, to become the monster. She can't have kids or a normal life either.
Widow isn't calling herself a monster because she can't have kids. She's saying that she's done terrible, monstrous things just like Banner, that the sterilization was a turning point that made her from a child into the monster she was trained to become. For Banner that moment that made him was the Gamma ray hit that turn him into the Hulk. For Widow it was the years of training, her first kill, and finally the sterilization that took away her future as anything but the assassin killer.
People with agendas have only managed to see "female character needs a man", but Widow feels a kinship with Banner because they both are looking for some kind of atonement for what they are and what they've done. Their close relationship (her as his handler) and the intense situations they've been through - well, intimacy happens, and they both want some basic human warmth and connection that their respective situations have denied them.
Do I think any of this was right or necessary for the film? No, definitely not, but if we read a little between the lines (if audiences can still do that), then I think Whedon is trying to do more here with the characters than just leave them as two dimensional cut-outs. It's just the harsh edits to get the shortened running time have left those who want to find something to be offended by this little nugget to shout about.
All the characters have their stories and fears, but for the most part they are cut. Banner and Widow want a normal life free of the killing. Stark wants an end to the fear that he can't protect the world and will get everyone killed. Cap mourns the life and the woman he lost years in the past. Hawkeye wants a world for his kids, a time when he can lay down his bow and live a simple life. Thor fears he can't protect Asgard.
Scarlet Witch reaches into their heads to show the audience who they are. It's all there, but the big cuts in the running time left the character parts as chopped up, disjointed scenes between the action set-pieces.