Heritability is a scary factor in deciding how intelligent groups of people are. Statistics can give us benefits in research, but when it comes to individual intelligence, Statistics lump people together in a way that takes away all individualism. Coupled with demographics, this can be a scary process that can lead to recism.
Yes, this is a very valid argument for racism, for example here in the United States. Most of the white Americans here in the United States are born naturally with a higher IQ on average that that of African American people. So it is a very valid argument to use.
No, the heritability of IQ is not an argument in support of racism, because there is no proof or evidence even that IQ is linked to race. There are many smart white people out there, but there are many not so smart ones too. The same is true for black people, Asians and whomever else. IQ and race are not related.
I do not believe the inheritability of IQ is an argument in support racist. I believe anyone who takes this position is simply grasping at straws attempting to justify their own racist beliefs. IQ tests are created by man and have no real meaning in basic human life. Racism can't be justified.
Although IQ can be inherited due to someone's parent's educational attainment, that is no excuse for racism. If anything, a higher IQ should be for more diversity and less racism in general. More diversity in human genetics means a greater chance of surviving a global calamity. Higher or lower IQs don't necessarily mean racism, although there is a greater divide between educational attainment and those who only graduate from high school.