vriska and dirk (at the beginning of their arcs) are both people who take “the ends justify the means” to its logical extreme
theyre both people who grew up from infancy under incredibly adverse circumstances and, instead of acknowledging that that adversity traumatized them, recontextualize their coping mechanisms and survival tactics as “strength”. vriska tells herself that her lusus turning her into a child soldier and constantly dangling the threat of death over her head made her a smarter, stronger, more cunning person. dirk tells himself that growing up isolated from any human contact and being forced to fend for himself against the elements and assassination attempts by the condesce made him capable, self-sufficient, and mature.
they think that adversity made them strong - pressure makes diamonds, steel sharpens steel - and that they are their best selves. and they love their friends (yes, even vriska - look at the way she talks to aradia or terezi), and they want whats best for them. specifically, dirk and vriska want what they think is best for their friends, regardless of their friends actual wants or needs. dirk and vriska think that adversity is what made them strong, so in order to empower their friends, dirk and vriska will be that adversity.
of course this fails because dirk and vriska 1. are stupid children, and 2. lack the social graces or understanding of interpersonal relationships to know when theyre pushing someone past their limits. the only real difference is that vriska is hyper-empathetic, whereas empathy for dirk is a learned skill - vriska has explosive episodes of rage that shes immediately consumed with guilt over, and dirk hurts people because he cant really understand when theyre expressing unease or discomfort
and they both have arcs that revolve around this architecture of strained, broken relationships and inflated egos crumbling around them. all of vriskas friends turn against her. dirks emotional inaccessibility is a prime contributing factor to the trickster clusterfuck. vriska, who thinks that she can handle everything, is killed by terezi in order to prevent a doomed timeline. dirk, who thinks that he can handle everything, is functionally neutered for the entire condesce/aranea conflict when jade teleports him to the furthest reaches of space.
post-retcon homestuck has a lot of flaws (ive written about this extensively before) and one of them is that while dirks arc gets a satisfying resolution, vriskas doesnt. dirk comes face-to-face with his own worst case scenario, how his mindset and behavior has the potential to damage people irreperably, and resolves to make amends and change. (vriska), when divorced from the environment of constant stress and violence that defined her childhood and shaped her as a person, opens up, lets herself be vulnerable, acknowledges her own flaws and shortcomings and ultimately reunites with the terezi from her native timeline. vriska prime doesnt have these same revelations about herself - yes, vriska prime and (vriska) are the same character, and (vriska) exists to show vriskas true nature and potential for introspection and self-awareness, but vriska prime is still exhibiting the flaws (vriska) overcame all the way through the end of homestuck. vriska comes SO fucking close to having a satisfying resolution, swerves, and misses it. thats the fault of bad writing, though.
ultimately though theres more than enough evidence of vriskas character to make her sympathetic and forgivable - more than dirk, even, id say - it takes a certain special kind of cognitive dissonance insist that one is guilty and the other is innocent