If you're doing anything other than passively buying index funds, you're probably screwing yourself, but your choice of broker is irrelevant.
As a small-time, retail investor, you are statistically guaranteed to make random, uninformed trades, and it is profitable for market makers to process them, in much the same way that it's profitable for a grocery store to sell you groceries. And much like the grocery store selling you potato chips, they make their money on volume, not on gouging you on the cost of staples.
Whether you should be buying those chips (or day trading AAPL) is a question for you and your dietician and/or investment advisor, but you don't need to worry about the price.
How are you guaranteed to make random uniformed trades? Moreover, you said above that you are only “probably” screwing yourself. And you’re right, unless you love investing and deeply care about making alpha, it’s probably not for you.
But the markets aren’t a random walk and even if you are just buying indices, you still have to actively manage them. Namely you have to decide asset allocation, leverage, industry, country exposure, etc. Also you have things like style exposure to consider as well. As such, there’s really no such thing as passive management.
Also, actively trading beta isn’t exactly the hardest thing in the world. Even though some players move extremely quickly over market news like Trump tweets, trade war announcements, etc, it still takes a couple days for all investors to react to the news. In fact, retail investors are often better positioned to quickly react as the slippage on their trades is non-existent for all but the most illiquid names.
In short, I wouldn’t recommend actively trading for most people. But those people are still going to need to choose some allocations and rebalance once in awhile. For those that are interested, retail alpha isn’t that hard to find, especially with leverage.
As a small-time, retail investor, you are statistically guaranteed to make random, uninformed trades, and it is profitable for market makers to process them, in much the same way that it's profitable for a grocery store to sell you groceries. And much like the grocery store selling you potato chips, they make their money on volume, not on gouging you on the cost of staples.
Whether you should be buying those chips (or day trading AAPL) is a question for you and your dietician and/or investment advisor, but you don't need to worry about the price.