yes i think that people are free to invest with any amount of discretionary income they have at their disposal, as far as that amount is coming from individuals discretionary income then there shouldnt be too much of a problem. because in bitcoin investment sometimes even when people are dcaing little by little and probably a particular week or month an extra or additional money comes to them and they finished sorting out their basic expenses they can decide to buy a lump sum with that additional cash that comes in for them either as a result of bonus they receive from work, or they win money from lottery or other sources. so its legal to invest with a good amount of cash as far as it is your discretionary income.
I think a person has complete freedom in their investment, and it is ultimately their own decision which method they will use. Some people are comfortable with DCA only, some want to use lump sum occasionally, and some can even mix the two.
My personal opinion is that when extra cash comes in, I think it is more logical to increase the DCA amount a little than to do a lump sum all at once. Because the biggest strength of regular DCA is that it gives the investor a habit, a rhythm, a system. If someone buys regularly every month or week, then he will worry less about market timing, and keep his accumulation process steady. Now let's say a person is buying $50 every week. Suddenly he gets $400 extra. If he wants, he can buy BTC at once with that $400, but that may reduce the focus on his regular buying system and increase the excitement. On the other hand, if he keeps a part of that extra cash and increases his weekly buys from $50 to $100 in the next 8 weeks, then he has used the extra cash at the same time, and his regular disciplined accumulation process remains intact.
However, I am not rejecting lump sums completely. If someone really wants to give a part of the extra cash in lump sums, then first half of the lump sum for experimental purposes, and the remaining half as regular DCA. In this, the investor gets some benefit from both sides.