Why did society point the finger at certain suspects?

http://www.casebook.org/suspects/
With many, if not all, of the Jack the Ripper suspects, there is very little strong evidence which can be classified as reliable for them. Instead, a lot of the evidence is merely down to presumption and interpretation. This makes it a near impossible task for us to ever be able to find the identity of the killer and there have been hundreds of suspects in the 120 years since the murders. So what is it that we look for when we're finding the murderer?

Some became suspects because of their occupation, Mortuary Assistant Robert Mann, may have got a thrill from working on the people he had himself killed just days earlier, or did mentally insane butcher Jacob Levy, continue the day job on his victims? Needless to say barber Aaron Kosminski would have been useful with sharp objects and who would suspect a Midwife Assistant if they were covered in blood, Constance Kent could have been the female ripper.

A large number of the suspects are known to have some sort of mental health issues, Levy being one example, or Montague John Druitt who committed suicide not long after the murders had taken place after suffering from depression like his mother and grandmother had done in previous years. James Kelly, escaped from a mental institution not long before the Whitechapel murders took place and was also known to have visited New York.

Or was it a foreigner? Seweryn Klosowski was born in Poland and poisoned three of his wives, Aaron Kosminski who was earlier mentioned was a Jew from Poland, Michael Ostrog came from Russia although was never convicted of a crime more serious than theft. Walter Sickert had Danish blood and was born in Germany, while there was even one suspect, Russian-born Alexander Pedachenko who may never have even existed.

Did we target foreigners because they have different cultures to ourselves and therefore we don't understand them? Was it easier to blame mental people as we could blame their illness as the reason for their behaviour? And was it easy to just blame someone who's occupation made them at ease with the use of blood and sharp objects? Because I think that despite all of these possibilities, it is just as likely that the murderer was someone who was English, appearing mentally sane and had a job that had absolutly nothing to do with blood, bodies or even knives!