If you can't trust your manager to take responsibility for the decision, then it's better to make a decision you're going to be held accountable for than to let your manager make the decision and then hold you accountable.
I've seen other engineers in the position where they give a risk analysis and warning in writing, and then shit hits the fan and they get fired. Maybe it doesn't happen immediately, maybe the reason they were fired isn't explicit, but the change in the manager's attitude toward the engineer traces back to when they did what the manager said.
There are also mangers who won't follow through on the tech debt part because they don't trust their engineers even if their engineers are trustworthy. When they discover that they can bypass testing by pulling the emergency lever, they'll start pulling it all the time because they see it as a way to get what those lazy engineers to do their jobs faster. And when tech debt catches up with you, bugs abound, and development slows to a crawl, the engineers get blamed.
Maybe you have a boss you can trust to take responsibility for their risky decisions. Maybe your boss trusts you when you say that paying down tech debt is necessary. But maybe your boss and their boss don't have the same relationship, and the shit rolls down hill.
Yes, I want to work in a trusting environment where my interests are aligned with doing what's best for my company, but an at-will employment capitalist economy doesn't always work that way. It's every man for himself at a fundamental level, and exceptions to that are too rare to make a blanket claim that people should just do what's best for their company.