Colbert brought Spicer onto the Emmy awards as a surprise and used him to poke at Trump.
It wasn't a great idea and it was fairly tone deaf. It was also one moment in 10 years of Colbert going in on Republicans and helping to educate young viewers on politics. Some people have decided to say, "Fuck Colbert," based on one decision they disagreed with, as if he went Bill Maher on everyone.
I generally agree with what Jason Isaacs said in his Instagram post but I also don't think it's that big of a deal in the long run. Certainly not enough for me to jump to "fuck Colbert." I don't expect perfection, I expect people to generally do the right thing and he does, 95% of the time.
The ease at which liberals can tell people who are on their side to "fuck off" because they do one thing disagreeable is really depressing and needs to change if we want to make legitimate pushes forward in 2018 and 2020. Look at their entire body of work, not singular moments.
For example, Kimmel having Spicer on just last week and taking a selfie doesn't make the impact of his multiple monologues on health care any less impactful.