Why you shouldn’t take profit is:
1. Using the money to actually spend it on unnecessary luxuries (emphasis on unnecessary, as there is nothing bad to get some luxury for your self).
If you make profits in investment and have nothing more in demand to use the money for than to spend it on your own self for pleasure, i dot see anything bad in it, when else do we have to eat the fruit of our labour if not now, at least what you're spending is not your actual investment, but from the interest made.
2. It is wrong to take profit and abandon it on fiat currency, that’s going from an asset with a store of value to one with devaluing characteristics.
If you may need to spend your profits on what is only acceptable in fiat, then why not, am sure an investor will not for the sake of holding exchange his bitcoin or any crypto to fiat, knowing how it could be affected by inflation as the value decreases over time.
4. lastly Buying Altcoins are not diversification means so do not take profit from bitcoin to buy Altcoins.
It could be a diversification, some times bitcoin may not be performing well and you got to discover that the altcoins are well to do, you can be profitable in them, only be selective in which altcoin youre going to invest in other to avoid shitcoins.