> Lorenzini stated: "It had been badly welded together about a third of the way down and couldn't stand the strain of the race. We discovered scratches on the crack in the steering rod. It seemed like the job had been done in a hurry but I can't say how long before the race. Someone had tried to smooth over the joint following the welding. I have never seen anything like it. I believe the rod was faulty and probably cracked even during the warm-up. Moments before the crash only a tiny piece was left connected and therefore the car didn't respond in the bend."
If that’s your bar for DIY stuff, you couldn’t do anything at all.
With enough time, everything will be messed up by a professional at some point.
If some electrician makes a mistake when wiring a house and it burns down, does that mean that I can never trust myself to wire something myself?
Arguably you have an advantage over the professionals because at least you’re motivated to do it properly because it’s your own life on the line.
Edit: for another half-serious analogy: if a professional race car driver ever crashes while driving on a regular road, does that mean I can’t drive myself? Because even a professional made a mistake while doing it, so how can I be trusted to do it better?
If done badly, yes. There are lots of competition cars (rally cars I have direct experience of) with modified and welded columns that haven't had issues in extreme circumstances. Providing the welding is done to a high standard it is more than strong enough.
Bear in mind that all modern steering columns have joints in them for crash safety reasons and they are often welded at the factory.
See the fatal accident of Ayrton Senna. Shortened and welded steering column was exactly the cause of the accident.