I think I may have figured out why so many people hate Samson.
In Inquisition, Samson's face was redesigned to make him have 2 physical attributes:
1- A devilish look, with long, thin, peeked eyebrows (much like Spock, from Star Trek), heavily lidded eyes, a downturned nose and a constant smirk (that make him look cynical all the time).
2- An overall air of bad health, typical of a junkie.
Based on the premise that people judge influenced heavily by appearance rather than true nature, I'd say the player is prone to hate him based on first impressions.
If we add to this the lack of vital information on his background in Inquisition, then you have players judging him as a degenerate, filthy templar who led the degradation of the "once noble and upstanding" Templar Order.
I REALLY find this odd because, in DA2, Samson is constantly complaining about people looking down on him and being insulted by being called a degenerate templar and an addict. He's offended to be considered a guttersnipe and strives very hard to be readmitted in the Order.
Which is why we come across him in Best Served Cold in Act 3. He's spent 6 years on the streets trying desperately to find a way to once more become a templar. He never once lost his pride and his willingness to serve.
And yet, "he's that filthy degenerate"...tough.