I think LAs are responsible for the majority of the negativity, personally.
First of all, LAs offer little to no help to a private tenant on the verge eviction - other than if you make yourself homeless by leaving before the courts, you can't go on the housing list. This in itself creates a breakdown in the relationship between tenant and LL. Tenants agree to leave after section 21, then refuse after approaching the LA for assistance.
They also offer no cooperation with the LL, if HB has been stopped for whatever reason. This makes the tenant look like a liar. I worked for an LA in the housing dept, and had to deal with an LL who had not received rent for a year. The tenant told him HB was stopped, he was trying to be fair and reasonable, but after a year became suspicious. He said if HB had been genuinely stopped, he'd likely continue renting out to her as its not her fault. But he only had her word for it, and LA obvs couldn't confirm due to data protection.
I looked on her account (I couldn't see anything to do with HB in my role just allocations) and could see she had phoned in several times, and been given the advice to stay put regardless of what happens, and only leave if/when it all went through the courts.
I can guarantee, if that tenant did ever leave, then that LL will never rent out to a benefit claimant again, due to the loss he incurred.
Almost every landlord I know has had a similar experience with renting out to benefits claimants, whether thats because HB has been stopped or not. I think rather than them having a negative view of claimants, they just don't want to end up dealing with the LA issues.
And no, not all benefits claimants are liars, obviously. But I do think a lot of people (employed or not) have cottoned on to being able to stay in a property rent free for some time, and take advantage.
Its just that someone in employment is generally(not absolutely!) less likely to have their income stopped abruptly, unlike someone on benefits (again an LA issue, they allow no adjusting period during sanctions, but tell the tenant to stay put rent free).
Of course, there are some prejudiced landlords, but the same can be said for all categories of people with people.
Whilst some say it should be illegal to not accept tenants on benefits, I also think it should be illegal to leave landlords without rent for 3+ months, and to have the LAs support in this.