Yea, buying aggressively is not wrong just that some folks always get it twisted, buying aggressively from your discretionary is not wrong but one thing an investor should not do is to be over aggressive even though it is from their discretionary because when you are over aggressive with your discretionary you will buy more than you are suppose to... and at this point in time it becomes wrong and bad because you are now going beyond your elastic limit hope you know what this means in strength of material.
Maybe, I will say that you don't understand the meaning of 'over aggressive buying' when you are buying with an amount within your discretionary income is not called over aggressive buying. It's when you buy with an amount beyond your discretionary income that is called over aggressive buying.
For example, if your discretionary income is $100, and you start buying bitcoin above $100 whenever, your discretionary income is available, you are buying over aggressively, and that will make you sell your bitcoin when it's not of your will because you are only gambling and not investing. When your needs arise, you will have to sell the bitcoin that you bought out of your discretionary income. You might sell at loss if bitcoin price is below your entry point. This is why one needs to be careful when buying aggressively so that you don't overdo it.
I agree with you and no wonder some folks panic or sell when their investment is not yet mature and I think the major reason why some of these folks buy more than what is in their discretionary is because of greed, wanting to have a big portfolio when they don't have what it takes to do that. I have really learnt something from this your post, at least I now know that investing beyond what is in one's discretionary is over aggressiveness which is a wrong move for an investor most especially those with little source of income.