"I would like some answers as to why people think UKIP are sinister"
I don't think the party is sinister exactly, I agree with some of their points but disagree with enough key ones that I would never vote for them. It doesn't help that they seem to have a higher percentage of arseholes than the other parties, though I am going to give them the benefit of the doubt this time and assume it's because their popularity has grown so fast they just wanted to contest as many seats as possible and therefore didn't vet people properly.
Reasons why I won't vote for them:
They want out of the EU and I think it would be a disaster if we left completely. I'd be happy if we managed to stay in the economic area and nothing else but realistically I don't think that will happen, and I'd rather be fully in than fully out.
They are against gay marriage, which makes them an automatic no for me.
There policy on asylum seekers leaves me feeling quite cold TBH. They want people held in secure detention centres (ie prisons) and limited rights to appeal. It's completely dehumanising to lock up people coming in from terrible circumstances and I think it is a very dangerous road to go down. I can see "limited right to appeal" becoming "no right to appeal" very fast and the entire system would be open to corruption, which would end up costing people their lives. I've also heard that asylum could be stopped from certain countries UKIP deems safe (can't find this on their website though so I'm unsure how accurate it is), which is completely wrong as living in a country can be perfectly safe for one person and a death sentence for another depending on circumstances.
They want to double the amount of prison spaces, whereas I personally think we already imprison people who have committed relatively minor offences far too often. If we create more prison spaces it will just lead to more people being sent there for relatively small crimes that IMO can be better dealt with in the community.
I hate there environmental policies. They want to support coal and oppose wind farms, it's like they actively want to speed up the destruction of the environment! I could sort of understand it if they wanted to have both but they seem to be objecting to renewable sources being used at all.
That's from about 5 minutes googling for the exact policies so I could easily have missed something but honestly, I'd be pretty scared for the UKs future if UKIP ever got to power.