My observation has been that most mainstream protestants have a “live and let live” attitude. They don’t try to convert you and they don’t want you trying to convert them. It seems that the more splits there have been in a denomination’s past, the more they reject Catholicism.
If you consider a person who was brought up say, Baptist, and has never been exposed to any other religion, but has been exposed to numerous ministers holding and preaching various anti-Catholic beliefs, it is reasonable to assume that they would assume a defensive posture when exposed to anything Catholic and would attack it using what they have been taught of the Bible. I was once in a discussion with a very active and devout lady about the importance of obedience in addition to faith (I tried not to use the word “works”), and when she got frustrated with me, she snipped “You either believe the word of God or you don’t.” When I quoted a few other Biblical passages in defense of my position, she informed me that those passages did not mean what I was reading into them. Some arguments you just can’t win.
The “higher” denominations such as Methodists and Lutherans are usually more accepting of Catholics but obviously don’t accept all our beliefs and will argue endlessly about details.
Then, there are the denominations such as SDA and JW who are openly and vehemently anti-Catholic. I guess some Baptists, since each church is totally independent, also fall into this group.
All in all, I would hesitate to characterize all protestants the same way. They differ a lot, depending mostly on what they have been taught.