That is so irritating on carrier branded firmware.
Assuming that you are using the stock Samsung Internet browser, go to...
Internet > Menu (3 bar, hamburger menu, bottom right) > Settings > Homepage > Custom page.. change it to what you like
What CSC code is your device on?
Go to... Settings > About phone > Software information > Service provider software version... (3 letter code, see screenshot)
BTU = stock unbranded firmware for the U.K. which I am on. So it is not Samsung forcing this on you but your carrier via your SIM card. I know it is not EE because they are my carrier on a BTU CSC code and they have not done that on my unbranded firmware.
I am guessing that even if you installed, say, Google Chrome, your carrier would hijack the Homepage as they used to do in the old Nokia days.
I can only but suggest that you contact whoever your carrier is and make your feelings known.
I agree with you walkerx. Three U.K. and other carriers should not hijack their customers browser homepage without their permission.
Their reply, I guess, will be along the lines that it is easy enough to change and that lots of their customers find that a Three homepage is very useful. It also means they can channel your browsing. Good luck in getting them to change this underhand procedure.