Regarding TMs, follow your common sense. All the dangerous acronyms are pretty well known, so choosing to reg one of them (like the IBM one) is obviously a risk.
As for the rest of acronyms, I think registering them without parking them (ie. no ads shown on the page) should be safe. Just try not to be too greedy with them. (ie. trying to sell a registered TM acronym to the company that owns it is stupid imo).
Regarding what you said
@photonmymind about why people don't care on TMs:
There are countries that don't follow the international TM laws (indonesia for example). There you can sell any name you want without fearing for the consequences.
Another reason is the quick flip. One can buy several TM names, sell as many as they can within a short time and then delete the ones that haven't been sold before anyone tries to go after them.
I haven't actually 'seen' such practice but it sounds quite feasible not to be true.
Personally I spend at least an hour on a daily basis to clean possible TM names from the list I'm about to do research on. Even when something slips through and I realise it's a TM, I promptly delete it. I delete it even if that costs me the registration I paid. Reputation is all we have in this business.