From my experience, observations, the following are how MAs are interpreted:
1. Newbs who just read a book or 2 on "how to make money trading...": They think buying/selling when prices cross MA will be good enough to quit their day jobs and make money, as long as they find the magic parameters.
2. Trading "Educators": "MAs are only useful if you use a shitload of them," e.g. have at least 6 of them so that you can create a kickass backtest curve to entice the above mentioned newbs into paying subscription fees.
3. Quants with PhD's, and maybe a year or 2 of losses: MAs alone are useless, the KEY is their slopes! Also, backtesting MA "strategies" is only useful if you optimize with "machine learning".
4. From the few seasoned traders I know, something I agree with: MAs are an OK, rough method for quantitative risk management. E.g. if you're bullish something, you could reduce exposure if it drops below MA, and put-it-back-on if it crosses back above. This way you reduce your chance of significant draw-downs, while minimizing opportunity cost.
On 1) Any MA can be made so it "crosses over", so that tell you it is relative. So therefore the notion of "crossing" is arbitrary, group thinking aside.
On 2) Back testing sucks with MAs because the reality of real time, intra-bar painting is never captured. Plus the obvious curve fitting to static data.
On 3) First and second derivative are relevant. If one does not know what that means they don't understand MA's represent beyond the MA part.
On 4) These people are not Newbies, and details of such a discussion is beyond the scope.