The issue is their legality under International Law. The West Bank was annexed by Israel after the 6 day war in 1967. Prior to that since 1948 it had been controlled by Jordan, though Jordan's annexation was not recognised Internationally except by the UK. Artcile 49(6) of the fourth Geneva convention prohibits states from transferring their own civilian populations into territories they occupy as a result of war:
https://ihl-databases.icrc.org/appl...6756482d86146898c125641e004aa3c5?OpenDocument
Israel is a party to the convention so the rule applies - though they have disputes it's application to the settlements. Article 8 of the Rome Statute of the International Criminal Court also declares transfer a war crime, but Israel has never ratified that treaty.
Interational bodies and UN organs are generally of the consensus that the settlements are in breach of this provision. The 2004 advisory opinion of the International Court of Justice provides at [120]:
http://www.icj-cij.org/docket/files/131/1671.pdf
Opponents of this view argue art 49(6) only applies to either forcible mass transfers or to situations where transfer causes displacement of local populations - they would argue that the settlements therefore don't breach the article as they are voluntary settlements and were not intended to displace Palestinians from the area.
Another, and in my opinion better, argument would be that the Oslo accords in leaving the issue of settlements to be resolved post their ratification represent Palestinians accepted the temporary presence of Israeli settlements pending further negotiation, and thus there is no basis for declaring them illegal.
As to whether the settlements are "dangerous, bigoted or hateful" (those are not the best terms to apply here) comes to a question as to the settlements affects on the human rights of Palestinians living in the West Bank. The Economic and Social council's 2005 report highlight discriminatory polices against Palestinians by the Israeli government, particuarly in relation to roads:
http://www.miftah.org/Doc/Reports/2005/G0511608.pdf
A Human Rights Council Report in 2013 also made conclusion that the settlements constituted breaches of rights to self-determination, non-discrimination, access to water and freedom of movement.
http://www.ohchr.org/Documents/HRBodies/HRCouncil/RegularSession/Session19/FFM/FFMSettlements.pdf