1) STT is very high, for intraday and overnight in cash too if you are holding for a few days only.
2) For intraday in stocks, Slippage cost - diff between entry price and filled price for entry + exit order can also be very high.
On average, it is equal or more than taxes+brokerage once you scale up. So simple estimation of cost = 2* costs.
3) And vs backtest, there can be further degradation due to data errors - entry/stop filled but does not show up in data.
So edge must be much more than cost. Its possible, but yeah govt takes away a large cut before you make money and then takes away another large cut once you make money ...
Or hold for longer periods, say using weekly charts or look at FnO overnight but that might need a lot of capital depending on how you trade. Or just give up, and look at investing + some technical rules if they help ...