Does "have at it" mean opposition?

CNN tweeted:

US Vice President Mike Pence and Democratic vice presidential nominee Kamala Harris will be separated by plexiglass at Wednesday night’s debate, a source says. The decision to enhance safety measures at the VP debate was met with mockery from Pence's team. "If Sen. Harris wants to use a fortress around herself, have at it," said spokeswoman Katie Miller, who herself tested positive for coronavirus in May.

A lot of people tweeted that Pence's compaign opposed Harris' request. Doesn't "have at it" mean "go ahead with it"? Why does it mean opposition? Thanks.

Solution 1:

"Have at it" does mean "go ahead with it" in this sentence. It does not mean opposition. The usage is similar to idioms like "be my guest".

For each, the tone matters: in some cases, it might indicate true welcoming. In others, it is said with a bit of sarcasm. I infer the sarcastic meaning here. Effectively, Miller is saying "go ahead and do something that I think makes you look silly." She is mocking the approach as unnecessary by using hyperbole in comparing it to a "fortress".