Its not bad to sample anything. Sampling the start of a track has only been looked down on because its so easy to do, as its the first thing that you hear so its the first thing anyone else with the same sample would of heard.
Its what you do with that sample that makes the difference. In this modern age the chances of finding an unused/rare sample is decreasing - personally ive given up caring if someones used it before and just treat them all like they have been used.
Ive got a bunch of samples on my computer that sound like like all they need is a regular boom-bap drum beat and to thicken the bass from the sample, but its way too easy + i feel like i havent done anything.
The point is, at least try to stay away from just using the raw melody directly from the sample by, choppin/cuting and if the sample is too prime to do any of that to, work into it, layer other parts of the song into it, maybe you'll get some nice vocals for a concept and DEFINITELY work the drums into it, if all else fails.