I'd say the love and affection for Britney has always outweighed any hatred across the board, but throughout her career, Britney has been hated for a myriad of reasons.
To begin with, the main reason for the hatred was her image being too **** and controversial for her young fans. Her image was considered highly inappropriate and this angered parents unbelievably so. They believed she was a terrible role model for their young children and was "everything wrong with America".
Further hatred then came around the time she split with JT - not only did this breakup cause a huge shift in her public image and the way she was perceived, but it was also around the time pop music was seen as "uncool" and people's tastes were shifting more towards rock and R&B. It was then uncool to like Britney's "superficial image" and musical output - people hopped ship to Avril Lavigne etc.
One of the biggest turning points, however, was when she started dating K-Fed and the years that followed. The Vegas wedding, the barefoot scandal, dressing like K-Fed along with Chaotic turned Britney into a trashy figure. People hated her and considered her a talentless hillbilly by this point. Not only did people see her as trashy, but she was overexposed, had oversaturated the tabloids and the general public were generally sick of her. She hated being in the limelight by this point and people HATED her being in the limelight.
In the Matt Lauer interview, he asks who her audience would be if she was to release further music. At that time, it was a question everyone was asking. Who still listened to Britney Spears? Her teen audience had grown up. Children were no longer interested. Adults weren't interested. For quite a while, it seemed that her musical career was essentially dead and she was no longer relevant to any demographic.
It's why a lot of fans feel like the breakdown, in a lot of ways, saved her career. It revitalised interest in her and solidified her status as an enduring pop culture icon. It's absolutely horrible to say that, but there's definitely some truth to it. For a long time, it felt like she'd come to the end of the road of her career with no turning back.
(I feel like I went on a tangent there. What was your question?)