Poll: did I have a right to honk my horn?

I was driving slightly over the speed limit (instead of going 55 I went 58) and this car merged right into my lane so I had to push on the breaks in order to not hit them and I honked my horn and got in the other lane. They didn’t have enough time to get in my lane safely without me having to push on the breaks at the last minute
Answers

duck you sucker!

Yes. Through traffic always has right of way. Anyone merging--off or on, or turning, must not impede flow of traffic. My horn is used almost as often as my brakes. I say. almost, as many times there isn't time to do both. Look out for idiots that take "offense" at your horn--don't chase them. Let them be babies.

polly

Yes. It's the car that's mergings responsibility to do it in a manner that's doesn't interfere with the traffic in the lane proper. You shouldn't have to speed up or slow down to let them in.