This site is aimed to give non-opinion based answers; this question is worded in a way that leads to opinions (“bad”). I will do my best to give a straight answer.
I would argue that it is safe to say that there is a lot of hidden politics in discussion of fiscal policy and government debt. If someone does not like policy X, and policy X is popular, it is politically easier to attack X’s effect on government debt than X itself. This could explain the tone of discussions you have read.
As you note, it would be possible for a government to set the interest rates on all of its debt if it borrows in a currency that it controls (via control of the central bank). The standard argument against such a policy is that by doing so, the central bank would lose control of inflation. (That is, it needs to be seen to have the flexibility to raise interest rates to keep expected inflation under control.) There’s a lot of different theoretical arguments to get to that result. (As a disclaimer, I would note that I disagree with them, so I will not attempt to present them.)
Unfortunately, these arguments are often based on cryptic mathematics. You could try asking another question specifically on that topic to get a further background. (I did a quick search, but the questions I saw had various issues. In order to get good answers, you need to ask a very specific question, and avoid introducing editorial comments, as answers end up responding to the editorial comments.)
The next line of attack is that by increasing debt, interest costs are rising (assuming interest rates are positive). This implies that these costs become an increasingly large part of the budget. Furthermore, overlapping generations models (OLG models), typically suggest that this results in generational unfairness. (Future generations are disadvantaged relative to the current generation.)
Finally, there is the “intertemporal governmental budget constraint.” This constraint - if it holds, which is unclear - suggests that governments will need future primary surpluses to match current debt levels. (The primary surplus is the budget balance excluding interest payments.) The theoretical status of the budget constraint is controversial, but one could argue that it is related in practice to the previous argument about interest payments.