Money is relative. If one country borrows beyond it's means, it's exchange rate will suffer making it's currency worth less against others. If several major countries borrow beyond their means, they're all in the same boat, so the balance of payments doesn't change between them.
At the start of the pandemic, the global economic organisations basically told all developed countries to spend "whatever it takes" to counter the virus, medically, scientifically and economically. When most or all countries are doing the same thing, because money is relative, no particular country suffers to the benefit of others.
At the moment, we're all in the same boat, so "printing money", or quantitive easing, or borrowing money, or whatever you want to call it is acceptable for the short term. BUT the time will come when the "old" rules come back into play. If the UK comes out of the pandemic with a healthy population and healthy economy, we'll be fine, especially if we come out of it healthier than some other similar economies. However, if other countries come out of it better, and we're left struggling, then our borrowing will be a millstone around our necks, our exchange rates will suffer, costs of borrowing may rise if our lenders see us as a risk, etc.
Basically, along with other major economies, we have to do what it takes today to keep the country moving. To avoid long term adverse consequences we really need to hit the ground running as soon as life returns to normal for our economy to stay similar or better than other major economies.