is it qood idea to use an Equalizer with amp

Let your ears answer the question. All in audio is about the ears. If it sounds better, it is for you and that is all the really counts. Don't let 'old wife's' tales rule.

If the equalization is done to a digital stream, from a Cd transport, and before it is decoded, it can be pretty clean.
If the analog signal is digitalized and decoded just to EQ it, maybe not so great.
For a CD setup where you have a DAC, then adding in a device like the Behringer DEQ2496 and adjusting the EQ, probably would do no harm, and could offer benefits.
For a standard mid fi system, an analog EQ device might be acceptable. For most high end systems, an analog EQ device would add far to much grunge to be acceptable

I have an EQ, Luxman G11 - completely recapped and brought back to spec. This was a $500 EQ in the day. I use it with my Cary tube preamp, Monarchy amps, Usher speakers. I have it connected to my system using a home brew selector box (like a tape loop) so I can remove it from the circuit entirely. Like using it for some poorly mixed material or live recordings where the bass and/or highs are rolled.
Even with the EQ in the circuit and set to neutral settings - very hard to detect. So, in my opinion they can be used in a high system but best have a set up where it can be isolated from the signal path

if most of your recordings are bad.

I disagree with you Elizabeth... have you actually tried all the various kinds of equalizers you've mentioned in a "high-end" system?

Have you owned a unit with advanced digital room correction like the Lyngdorf or DEQ units? Have you used the Behringer DEQ2496 full-range in your system? And have you tried a unit like a basic DBX 1231 in balanced mode in a high-end system?

I can say that in my system the dbx 1231 sounded very clean, low-noise, and musical with no apparent grunge. Playing the system in my large room without EQ makes no sense. The dbx only costs about $350 and will work very well for those folks who just require a modicum of EQ and don't have the funds for something like a Lyngdorf, which works even better but costs much more. I've not used the Behringer DEQ2496. I've heard some say it's good for bass EQ and for its built-in RTA, but maybe not great for a full-range EQ. But I haven't heard it with my own ears in my system so I can't confirm that.

I'd be curious to hear of your actual use of the EQ's you've mentioned in your own system, because your conclusions/assessments don't align with my experience.