Blood prejudice is widely accepted
Someone like Lord Voldemort does not develop in a vacuum. Voldemort was a wizard of formidable skill, but by himself he was simply one person. He could not have led a campaign of terror and murder against Muggles and Muggle-borns, nor overthrown the Ministry, without widespread support.
How was Voldemort able to recruit dozens of Death Eaters? How was he able to maintain control over the Ministry of Magic even after he had turned into an obviously anti-Muggle apparatus?
Because prejudice against Muggles was already deeply ingrained in the magical world.
You didn’t need to be mad (Bellatrix Lestrange, Crouch Jr.) to join Voldemort’s side. The Death Eaters counted in their ranks members of some of the oldest, most respectable pureblood families: Lucius Malfoy, Bellatrix Lestrange. People bearing the names Avery, Black, Rosier, Carrow.
These were the pillars of society—and they were sufficiently devoted to pureblood supremacy that they were willing to risk it all at the side of a murderous psychopath.
Even people who were vehemently opposed to Voldemort were likely to show prejudice against Muggle, Muggle-borns, or non-human magical creatures.
For example, Cornelius Fudge:
“You are blinded,” said Dumbledore, his voice rising now, the aura of
power around him palpable, his eyes blazing once more, “by the love of
the office you hold, Cornelius! You place too much importance, and you
always have done, on the so-called purity of blood! You fail to
recognize that it matters not what someone is born, but what they grow
to be! Your dementor has just destroyed the last remaining member of a
pure-blood family as old as any — and see what that man chose to make
of his life!”
—Harry Potter and the Goblet of Fire
Or Horace Slughorn:
“Your mother was Muggle-born, of course. Couldn’t believe it when I
found out. Thought she must have been pure-blood, she was so good.”
“One of my best friends is Muggle-born,” said Harry, “and she’s the
best in our year.”
“Funny how that sometimes happens, isn’t it?” said Slughorn.
—Harry Potter and the Half-Blood Prince
Even Arthur Weasley, the drafter of the Muggle Protection Act and a committed opponent of pureblood supremacy, sometimes displayed a condescending and paternalistic attitude toward Muggles:
“Fascinating!” he would say as Harry talked him through using a
telephone. “Ingenious, really, how many ways Muggles have found of
getting along without magic.”
—Harry Potter and the Chamber of Secrets
As does Molly Weasley, while also hinting at the prevalence of such attitudes in the broader society:
When at last they were all in the car, Mrs. Weasley glanced into the
back seat, where Harry, Ron, Fred, George, and Percy were all sitting
comfortably side by side, and said, “Muggles do know more than we give
them credit for, don’t they?”
—Harry Potter and the Chamber of Secrets
Voldemort did not merely target Muggle-borns, Muggles, and those who supported them. He killed anyone who got in his way, anyone who spoke out against him. And given that his goals included taking over the Ministry of Magic through force, and potentially eventually revealing witches and wizards to Muggles, the list of people who opposed him would have included an enormous number of people with blood prejudice of their own.
So of course their children and relatives would hate Voldemort. He killed their families. But that doesn’t mean they disagreed with all his ideas.
Draco Malfoy mainly expressed pureblood supremacist ideals, as well as ideas about the superiority of wizards and witches over Muggles. As such, there would really be little for many witches and wizards to disagree with, even those who had seen family die at Voldemort’s hands.
Still, why didn’t the less prejudiced people get into fights with Malfoy?
They did! Hermione, Harry, and Ron got into fights with Malfoy all the time, and so might have many other people.
- Hermione punched Malfoy in the face in Prisoner of Azkaban
- Harry tried to fight a duel with Malfoy in Sorcerer’s Stone
- Ron hexed Malfoy when he used a slur against Muggle-borns in Chamber of Secrets
And all this before Voldemort even returned. There was no love lost between Malfoy and many other students.
Nonetheless, many people might have been discouraged from seeking fights with Malfoy, both from fear of punishment by teachers, and fear of retaliation or censure, either by their more-prejudiced peers, or by Crabbe and Goyle.