...of other countries, unless it's something I agree with"
To call this idea "dangerous" or a "slippery slope" would be an understatement. If the UN is wrong, it's wrong. It's that simple. By endorsing its authority the one time you agree with it, you are endorsing the very existence of an immoral institution and its actions the other 99% of the time.
Tu ne cede malis sed contra audentior ito