The idea that those wishing to cause harm can just use knives or cars simply doesn’t stand up. There’s two crucial distinctions: Firstly, cars and knives are common and necessary everyday objects. You can require licenses and not sell knives to children, but there’s no reasonable way to stop people misusing them. The same cannot be said for guns, the sole purpose of which is it to kill.
Secondly, a country where criminals and terrorist use knives and cars instead of guns is far safer, to a huge degree. For example, the UK has a high Islamic terrorist threat, but the death toll is relatively low. There have been two notable suicide bomb attacks with large casualty counts, but that’s a seperate issue, as people make their own bombs, unlike guns. The death toll from attacks not using bombs is much lower than they would have been had guns been available. San Bernandino had a higher casualty toll than Woolwich, Borough Market & Westminster combined, not to mention many failed attempts. The difference is guns.