The process and FS isolation also make sysadmin-me all tingly inside. That way you can't hose up anybody else's clean install either (even if you're compromised).
As a side note, on mac, the VM that runs docker containers requires less ram and CPU than Hipchat. Go figure.
But I understand. If the workflow works for you and/or your team, well, what's the problem? It's working!
Manually installed packages are already segregated and can be uninstalled ya know. Might be a problem if you have no admin skills.
I think you may be the one without admin skills if you think working on your system Python is anything except reckless. No one cares that you have 20 years of doing it like that, it's a poor argument and shows up a really bad attitude.
On the contrary, if it rarely to never happens compared to the effort involved, it's not "reckless" at all, but a tradeoff. The site package folders are a simple path of files/folders, not hard to reason about. Nothing gets "hosed" without your participation. No need to live in mortal fear. In other words the cure is as bad as the disease.
The truth is that venvs are a hack with a lot fewer use cases now that user packages at the low-end and containers at the mid/high-end are now ubiquitous.
Honestly newbies would be a lot better off just avoiding venvs entirely. I make an exception for pipenv when appropriate since it hides the complexity as well as possible.